BasicPrelude

basic-prelude-0.7.0: An enhanced core prelude; a common foundation for alternate preludes.

Safe Haskell | None
Language | Haskell2010

BasicPrelude

Contents

- Module exports
  - Folds and traversals
- Enhanced exports
  - Simpler name for a typeclassed operation
  - Strict implementation
  - Text for Read and Show operations
  - FilePath for file operations
- Text exports
  - Text operations (Pure)
  - Text operations (IO)
- Miscellaneous prelude re-exports
  - Math
  - Show and Read
  - IO operations

Description

BasicPrelude mostly re-exports several key libraries in their entirety. The exception is Data.List, where various functions are replaced by similar versions that are either generalized, operate on Text, or are implemented strictly.

Synopsis

- module CorePrelude
- (!?) :: [a] -> Int -> Maybe a
- data List a
- unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
- sortOn :: Ord b => (a -> b) -> [a] -> [a]
- transpose :: [[a]] -> [[a]]
- sortBy :: (a -> a -> Ordering) -> [a] -> [a]
- cycle :: HasCallStack => [a] -> [a]
- filter :: (a -> Bool) -> [a] -> [a]
- zip :: [a] -> [b] -> [(a, b)]
- head :: HasCallStack => [a] -> a
- uncons :: [a] -> Maybe (a, [a])
- unsnoc :: [a] -> Maybe ([a], a)
- tail :: HasCallStack => [a] -> [a]
- last :: HasCallStack => [a] -> a
- init :: HasCallStack => [a] -> [a]
- null :: Foldable t => t a -> Bool
- length :: Foldable t => t a -> Int
- foldl1' :: HasCallStack => (a -> a -> a) -> [a] -> a
- scanl :: (b -> a -> b) -> b -> [a] -> [b]
- scanl1 :: (a -> a -> a) -> [a] -> [a]
- scanl' :: (b -> a -> b) -> b -> [a] -> [b]
- scanr :: (a -> b -> b) -> b -> [a] -> [b]
- scanr1 :: (a -> a -> a) -> [a] -> [a]
- iterate :: (a -> a) -> a -> [a]
- iterate' :: (a -> a) -> a -> [a]
- repeat :: a -> [a]
- replicate :: Int -> a -> [a]
- takeWhile :: (a -> Bool) -> [a] -> [a]
- dropWhile :: (a -> Bool) -> [a] -> [a]
- take :: Int -> [a] -> [a]
- drop :: Int -> [a] -> [a]
- splitAt :: Int -> [a] -> ([a], [a])
- span :: (a -> Bool) -> [a] -> ([a], [a])
- break :: (a -> Bool) -> [a] -> ([a], [a])
- reverse :: [a] -> [a]
- and :: Foldable t => t Bool -> Bool
- or :: Foldable t => t Bool -> Bool
- any :: Foldable t => (a -> Bool) -> t a -> Bool
- all :: Foldable t => (a -> Bool) -> t a -> Bool
- notElem :: (Foldable t, Eq a) => a -> t a -> Bool
- lookup :: Eq a => a -> [(a, b)] -> Maybe b
- concatMap :: Foldable t => (a -> [b]) -> t a -> [b]
- (!!) :: HasCallStack => [a] -> Int -> a
- zip3 :: [a] -> [b] -> [c] -> [(a, b, c)]
- zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
- zipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]
- unzip :: [(a, b)] -> ([a], [b])
- unzip3 :: [(a, b, c)] -> ([a], [b], [c])
- find :: Foldable t => (a -> Bool) -> t a -> Maybe a
- dropWhileEnd :: (a -> Bool) -> [a] -> [a]
- stripPrefix :: Eq a => [a] -> [a] -> Maybe [a]
- elemIndex :: Eq a => a -> [a] -> Maybe Int
- elemIndices :: Eq a => a -> [a] -> [Int]
- findIndex :: (a -> Bool) -> [a] -> Maybe Int
- findIndices :: (a -> Bool) -> [a] -> [Int]
- isPrefixOf :: Eq a => [a] -> [a] -> Bool
- isSuffixOf :: Eq a => [a] -> [a] -> Bool
- isInfixOf :: Eq a => [a] -> [a] -> Bool
- nub :: Eq a => [a] -> [a]
- nubBy :: (a -> a -> Bool) -> [a] -> [a]
- delete :: Eq a => a -> [a] -> [a]
- deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]
- (\\) :: Eq a => [a] -> [a] -> [a]
- union :: Eq a => [a] -> [a] -> [a]
- unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
- intersect :: Eq a => [a] -> [a] -> [a]
- intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
- intersperse :: a -> [a] -> [a]
- partition :: (a -> Bool) -> [a] -> ([a], [a])
- insert :: Ord a => a -> [a] -> [a]
- insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a]
- genericLength :: Num i => [a] -> i
- genericTake :: Integral i => i -> [a] -> [a]
- genericDrop :: Integral i => i -> [a] -> [a]
- genericSplitAt :: Integral i => i -> [a] -> ([a], [a])
- genericIndex :: Integral i => [a] -> i -> a
- genericReplicate :: Integral i => i -> a -> [a]
- zip4 :: [a] -> [b] -> [c] -> [d] -> [(a, b, c, d)]
- zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a, b, c, d, e)]
- zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [(a, b, c, d, e, f)]
- zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [(a, b, c, d, e, f, g)]
- zipWith4 :: (a -> b -> c -> d -> e) -> [a] -> [b] -> [c] -> [d] -> [e]
- zipWith5 :: (a -> b -> c -> d -> e -> f) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f]
- zipWith6 :: (a -> b -> c -> d -> e -> f -> g) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g]
- zipWith7 :: (a -> b -> c -> d -> e -> f -> g -> h) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [h]
- unzip4 :: [(a, b, c, d)] -> ([a], [b], [c], [d])
- unzip5 :: [(a, b, c, d, e)] -> ([a], [b], [c], [d], [e])
- unzip6 :: [(a, b, c, d, e, f)] -> ([a], [b], [c], [d], [e], [f])
- unzip7 :: [(a, b, c, d, e, f, g)] -> ([a], [b], [c], [d], [e], [f], [g])
- deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
- group :: Eq a => [a] -> [[a]]
- groupBy :: (a -> a -> Bool) -> [a] -> [[a]]
- inits :: [a] -> [[a]]
- tails :: [a] -> [[a]]
- subsequences :: [a] -> [[a]]
- permutations :: [a] -> [[a]]
- sort :: Ord a => [a] -> [a]
- singleton :: a -> [a]
- mapAccumL :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b)
- mapAccumR :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b)
- isSubsequenceOf :: Eq a => [a] -> [a] -> Bool
- class Applicative m => Monad (m :: Type -> Type) where
  - (>>=) :: m a -> (a -> m b) -> m b
  - (>>) :: m a -> m b -> m b
  - return :: a -> m a
- class Functor (f :: Type -> Type) where
  - fmap :: (a -> b) -> f a -> f b
  - (<$) :: a -> f b -> f a
- class Monad m => MonadFail (m :: Type -> Type) where
  - fail :: String -> m a
- guard :: Alternative f => Bool -> f ()
- join :: Monad m => m (m a) -> m a
- class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) where
  - mzero :: m a
  - mplus :: m a -> m a -> m a
- (=<<) :: Monad m => (a -> m b) -> m a -> m b
- when :: Applicative f => Bool -> f () -> f ()
- liftM :: Monad m => (a1 -> r) -> m a1 -> m r
- liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
- liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r
- liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r
- liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r
- ap :: Monad m => m (a -> b) -> m a -> m b
- void :: Functor f => f a -> f ()
- mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m ()
- forM_ :: (Foldable t, Monad m) => t a -> (a -> m b) -> m ()
- sequence_ :: (Foldable t, Monad m) => t (m a) -> m ()
- msum :: (Foldable t, MonadPlus m) => t (m a) -> m a
- forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b)
- filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a]
- (>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c
- (<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c
- forever :: Applicative f => f a -> f b
- mapAndUnzipM :: Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c])
- zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c]
- zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m ()
- foldM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b
- foldM_ :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m ()
- replicateM :: Applicative m => Int -> m a -> m [a]
- replicateM_ :: Applicative m => Int -> m a -> m ()
- unless :: Applicative f => Bool -> f () -> f ()
- (<$!>) :: Monad m => (a -> b) -> m a -> m b
- mfilter :: MonadPlus m => (a -> Bool) -> m a -> m a
- class Foldable (t :: Type -> Type) where
  - foldMap :: Monoid m => (a -> m) -> t a -> m
  - foldr :: (a -> b -> b) -> b -> t a -> b
  - foldr' :: (a -> b -> b) -> b -> t a -> b
  - foldl :: (b -> a -> b) -> b -> t a -> b
  - foldl' :: (b -> a -> b) -> b -> t a -> b
  - foldr1 :: (a -> a -> a) -> t a -> a
  - foldl1 :: (a -> a -> a) -> t a -> a
- elem :: (Foldable t, Eq a) => a -> t a -> Bool
- maximum :: (Foldable t, Ord a) => t a -> a
- minimum :: (Foldable t, Ord a) => t a -> a
- traverse_ :: (Foldable t, Applicative f) => (a -> f b) -> t a -> f ()
- sequenceA_ :: (Foldable t, Applicative f) => t (f a) -> f ()
- for_ :: (Foldable t, Applicative f) => t a -> (a -> f b) -> f ()
- maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a
- minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a
- class (Functor t, Foldable t) => Traversable (t :: Type -> Type) where
  - traverse :: Applicative f => (a -> f b) -> t a -> f (t b)
  - sequenceA :: Applicative f => t (f a) -> f (t a)
  - mapM :: Monad m => (a -> m b) -> t a -> m (t b)
  - sequence :: Monad m => t (m a) -> m (t a)
- for :: (Traversable t, Applicative f) => t a -> (a -> f b) -> f (t b)
- map :: Functor f => (a -> b) -> f a -> f b
- empty :: Monoid w => w
- (++) :: Monoid w => w -> w -> w
- concat :: Monoid w => [w] -> w
- intercalate :: Monoid w => w -> [w] -> w
- sum :: (Foldable f, Num a) => f a -> a
- product :: (Foldable f, Num a) => f a -> a
- tshow :: Show a => a -> Text
- fromShow :: (Show a, IsString b) => a -> b
- read :: Read a => Text -> a
- readIO :: (MonadIO m, Read a) => Text -> m a
- readFile :: MonadIO m => FilePath -> m Text
- writeFile :: MonadIO m => FilePath -> Text -> m ()
- appendFile :: MonadIO m => FilePath -> Text -> m ()
- lines :: Text -> [Text]
- words :: Text -> [Text]
- unlines :: [Text] -> Text
- unwords :: [Text] -> Text
- textToString :: Text -> String
- ltextToString :: LText -> String
- fpToText :: FilePath -> Text
- fpFromText :: Text -> FilePath
- fpToString :: FilePath -> String
- encodeUtf8 :: Text -> ByteString
- decodeUtf8 :: ByteString -> Text
- getLine :: MonadIO m => m Text
- getContents :: MonadIO m => m LText
- interact :: MonadIO m => (LText -> LText) -> m ()
- gcd :: Integral a => a -> a -> a
- lcm :: Integral a => a -> a -> a
- class Show a where
  - showsPrec :: Int -> a -> ShowS
  - show :: a -> String
  - showList :: [a] -> ShowS
- type ShowS = String -> String
- shows :: Show a => a -> ShowS
- showChar :: Char -> ShowS
- showString :: String -> ShowS
- showParen :: Bool -> ShowS -> ShowS
- type ReadS a = String -> [(a, String)]
- readsPrec :: Read a => Int -> ReadS a
- readList :: Read a => ReadS [a]
- reads :: Read a => ReadS a
- readParen :: Bool -> ReadS a -> ReadS a
- lex :: ReadS String
- readMay :: Read a => Text -> Maybe a
- getChar :: MonadIO m => m Char
- putChar :: MonadIO m => Char -> m ()
- readLn :: (MonadIO m, Read a) => m a

# Module exports

module CorePrelude

(!?) :: [a] -> Int -> Maybe a infixl 9 #

List index (subscript) operator, starting from 0. Returns `Nothing` if the index is out of bounds

This is the total variant of the partial `!!` operator.

WARNING: This function takes linear time in the index.

#### Examples

Expand

    >>> ['a', 'b', 'c'] !? 0
    Just 'a'

    >>> ['a', 'b', 'c'] !? 2
    Just 'c'

    >>> ['a', 'b', 'c'] !? 3
    Nothing

    >>> ['a', 'b', 'c'] !? (-1)
    Nothing

data List a #

The builtin linked list type.

In Haskell, lists are one of the most important data types as they are often used analogous to loops in imperative programming languages. These lists are singly linked, which makes them unsuited for operations that require \(\mathcal{O}(1)\) access. Instead, they are intended to be traversed.

You can use `List a` or `[a]` in type signatures:

    length :: [a] -> Int

or

    length :: List a -> Int

They are fully equivalent, and `List a` will be normalised to `[a]`.

#### Usage

Lists are constructed recursively using the right-associative constructor operator (or cons) `(:) :: a -> [a] -> [a]`, which prepends an element to a list, and the empty list `[]`.

    (1 : 2 : 3 : []) == (1 : (2 : (3 : []))) == [1, 2, 3]

Lists can also be constructed using list literals of the form `[x_1, x_2, ..., x_n]` which are syntactic sugar and, unless `-XOverloadedLists` is enabled, are translated into uses of `(:)` and `[]`

`String` literals, like `"I 💜 hs"`, are translated into Lists of characters, `['I', ' ', '💜', ' ', 'h', 's']`.

#### Implementation

Expand

Internally and in memory, all the above are represented like this, with arrows being pointers to locations in memory.

    ╭───┬───┬──╮   ╭───┬───┬──╮   ╭───┬───┬──╮   ╭────╮
    │(:)│   │ ─┼──>│(:)│   │ ─┼──>│(:)│   │ ─┼──>│ [] │
    ╰───┴─┼─┴──╯   ╰───┴─┼─┴──╯   ╰───┴─┼─┴──╯   ╰────╯
          v              v              v
          1              2              3

#### Examples

Expand

    >>> ['H', 'a', 's', 'k', 'e', 'l', 'l']
    "Haskell"

    >>> 1 : [4, 1, 5, 9]
    [1,4,1,5,9]

    >>> [] : [] : []
    [[],[]]

Since: ghc-prim-0.10.0

#### Instances

Instances details

MonadZip [] | Since: base-4.3.1.0
Instance details Defined in Control.Monad.Zip Methods mzip :: [a] -> [b] -> [(a, b)] # mzipWith :: (a -> b -> c) -> [a] -> [b] -> [c] # munzip :: [(a, b)] -> ([a], [b]) #
Eq1 [] | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftEq :: (a -> b -> Bool) -> [a] -> [b] -> Bool #
Ord1 [] | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftCompare :: (a -> b -> Ordering) -> [a] -> [b] -> Ordering #
Read1 [] | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS [a] # liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [[a]] # liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [a] # liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [[a]] #
Show1 [] | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Classes Methods liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> [a] -> ShowS # liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [[a]] -> ShowS #
Alternative [] | Combines lists by concatenation, starting from the empty list. @since base-2.01
Instance details Defined in GHC.Internal.Base Methods empty :: [a] # (<|>) :: [a] -> [a] -> [a] # some :: [a] -> [[a]] # many :: [a] -> [[a]] #
Applicative [] | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods pure :: a -> [a] # (<*>) :: [a -> b] -> [a] -> [b] # liftA2 :: (a -> b -> c) -> [a] -> [b] -> [c] # (*>) :: [a] -> [b] -> [b] # (<*) :: [a] -> [b] -> [a] #
Functor [] | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> [a] -> [b] # (<$) :: a -> [b] -> [a] #
Monad [] | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods (>>=) :: [a] -> (a -> [b]) -> [b] # (>>) :: [a] -> [b] -> [b] # return :: a -> [a] #
MonadPlus [] | Combines lists by concatenation, starting from the empty list. @since base-2.01
Instance details Defined in GHC.Internal.Base Methods mzero :: [a] # mplus :: [a] -> [a] -> [a] #
MonadFail [] | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Control.Monad.Fail Methods fail :: String -> [a] #
Foldable [] | @since base-2.01
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => [m] -> m # foldMap :: Monoid m => (a -> m) -> [a] -> m # foldMap' :: Monoid m => (a -> m) -> [a] -> m # foldr :: (a -> b -> b) -> b -> [a] -> b # foldr' :: (a -> b -> b) -> b -> [a] -> b # foldl :: (b -> a -> b) -> b -> [a] -> b # foldl' :: (b -> a -> b) -> b -> [a] -> b # foldr1 :: (a -> a -> a) -> [a] -> a # foldl1 :: (a -> a -> a) -> [a] -> a # toList :: [a] -> [a] # null :: [a] -> Bool # length :: [a] -> Int # elem :: Eq a => a -> [a] -> Bool # maximum :: Ord a => [a] -> a # minimum :: Ord a => [a] -> a # sum :: Num a => [a] -> a # product :: Num a => [a] -> a #
Traversable [] | @since base-2.01
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> [a] -> f [b] # sequenceA :: Applicative f => [f a] -> f [a] # mapM :: Monad m => (a -> m b) -> [a] -> m [b] # sequence :: Monad m => [m a] -> m [a] #
Hashable1 [] |
Instance details Defined in Data.Hashable.Class Methods liftHashWithSalt :: (Int -> a -> Int) -> Int -> [a] -> Int #
Generic1 [] |
Instance details Defined in GHC.Internal.Generics Associated Types
type Rep1 [] | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics type Rep1 [] = D1 ('MetaData "List" "GHC.Types" "ghc-prim" 'False) (C1 ('MetaCons "[]" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons ":" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1 :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec1 [])))
Methods from1 :: [a] -> Rep1 [] a # to1 :: Rep1 [] a -> [a] #
IsChar c => PrintfArg [c] | Since: base-2.1
Instance details Defined in Text.Printf Methods formatArg :: [c] -> FieldFormatter # parseFormat :: [c] -> ModifierParser #
IsChar c => PrintfType [c] | Since: base-2.1
Instance details Defined in Text.Printf Methods spr :: String -> [UPrintf] -> [c]
Monoid [a] | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods mempty :: [a] # mappend :: [a] -> [a] -> [a] # mconcat :: [[a]] -> [a] #
Semigroup [a] | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods (<>) :: [a] -> [a] -> [a] # sconcat :: NonEmpty [a] -> [a] # stimes :: Integral b => b -> [a] -> [a] #
a ~ Char => IsString [a] | `(a ~ Char)` context was introduced in `4.9.0.0` @since base-2.01
Instance details Defined in GHC.Internal.Data.String Methods fromString :: String -> [a] #
Generic [a] |
Instance details Defined in GHC.Internal.Generics Associated Types
type Rep [a] | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics type Rep [a] = D1 ('MetaData "List" "GHC.Types" "ghc-prim" 'False) (C1 ('MetaCons "[]" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons ":" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a) :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 [a])))
Methods from :: [a] -> Rep [a] x # to :: Rep [a] x -> [a] #
IsList [a] | @since base-4.7.0.0
Instance details Defined in GHC.Internal.IsList Associated Types
type Item [a] |
Instance details Defined in GHC.Internal.IsList type Item [a] = a
Methods fromList :: [Item [a]] -> [a] # fromListN :: Int -> [Item [a]] -> [a] # toList :: [a] -> [Item [a]] #
Read a => Read [a] | @since base-2.01
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS [a] # readList :: ReadS [[a]] # readPrec :: ReadPrec [a] # readListPrec :: ReadPrec [[a]] #
Show a => Show [a] | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> [a] -> ShowS # show :: [a] -> String # showList :: [[a]] -> ShowS #
Eq a => Eq [a] |
Instance details Defined in GHC.Classes Methods (==) :: [a] -> [a] -> Bool # (/=) :: [a] -> [a] -> Bool #
Ord a => Ord [a] |
Instance details Defined in GHC.Classes Methods compare :: [a] -> [a] -> Ordering # (<) :: [a] -> [a] -> Bool # (<=) :: [a] -> [a] -> Bool # (>) :: [a] -> [a] -> Bool # (>=) :: [a] -> [a] -> Bool # max :: [a] -> [a] -> [a] # min :: [a] -> [a] -> [a] #
Hashable a => Hashable [a] |
Instance details Defined in Data.Hashable.Class Methods hashWithSalt :: Int -> [a] -> Int # hash :: [a] -> Int #
type Rep1 [] | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics type Rep1 [] = D1 ('MetaData "List" "GHC.Types" "ghc-prim" 'False) (C1 ('MetaCons "[]" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons ":" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1 :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec1 [])))
type Rep [a] | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics type Rep [a] = D1 ('MetaData "List" "GHC.Types" "ghc-prim" 'False) (C1 ('MetaCons "[]" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons ":" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a) :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 [a])))
type Item [a] |
Instance details Defined in GHC.Internal.IsList type Item [a] = a

unfoldr :: (b -> Maybe (a, b)) -> b -> [a] #

The `unfoldr` function is a `dual' to `foldr`: while `foldr` reduces a list to a summary value, `unfoldr` builds a list from a seed value. The function takes the element and returns `Nothing` if it is done producing the list or returns `Just` `(a,b)`, in which case, `a` is a prepended to the list and `b` is used as the next element in a recursive call. For example,

    iterate f == unfoldr (\x -> Just (x, f x))

In some cases, `unfoldr` can undo a `foldr` operation:

    unfoldr f' (foldr f z xs) == xs

if the following holds:

    f' (f x y) = Just (x,y)
    f' z       = Nothing

#### Laziness

Expand

    >>> take 1 (unfoldr (\x -> Just (x, undefined)) 'a')
    "a"

#### Examples

Expand

    >>> unfoldr (\b -> if b == 0 then Nothing else Just (b, b-1)) 10
    [10,9,8,7,6,5,4,3,2,1]

    >>> take 10 $ unfoldr (\(x, y) -> Just (x, (y, x + y))) (0, 1)
    [0,1,1,2,3,5,8,13,21,54]

sortOn :: Ord b => (a -> b) -> [a] -> [a] #

Sort a list by comparing the results of a key function applied to each element. ``sortOn` f` is equivalent to ``sortBy` (`comparing` f)`, but has the performance advantage of only evaluating `f` once for each element in the input list. This is called the decorate-sort-undecorate paradigm, or Schwartzian transform.

Elements are arranged from lowest to highest, keeping duplicates in the order they appeared in the input.

The argument must be finite.

#### Examples

Expand

    >>> sortOn fst [(2, "world"), (4, "!"), (1, "Hello")]
    [(1,"Hello"),(2,"world"),(4,"!")]

    >>> sortOn length ["jim", "creed", "pam", "michael", "dwight", "kevin"]
    ["jim","pam","creed","kevin","dwight","michael"]

#### Performance notes

Expand

This function minimises the projections performed, by materialising the projections in an intermediate list.

For trivial projections, you should prefer using `sortBy` with `comparing`, for example:

    >>> sortBy (comparing fst) [(3, 1), (2, 2), (1, 3)]
    [(1,3),(2,2),(3,1)]

Or, for the exact same API as `sortOn`, you can use `sortBy . comparing`:

    >>> (sortBy . comparing) fst [(3, 1), (2, 2), (1, 3)]
    [(1,3),(2,2),(3,1)]

@since base-4.8.0.0

transpose :: [[a]] -> [[a]] #

The `transpose` function transposes the rows and columns of its argument.

#### Laziness

Expand

`transpose` is lazy in its elements

    >>> take 1 (transpose ['a' : undefined, 'b' : undefined])
    ["ab"]

#### Examples

Expand

    >>> transpose [[1,2,3],[4,5,6]]
    [[1,4],[2,5],[3,6]]

If some of the rows are shorter than the following rows, their elements are skipped:

    >>> transpose [[10,11],[20],[],[30,31,32]]
    [[10,20,30],[11,31],[32]]

For this reason the outer list must be finite; otherwise `transpose` hangs:

    >>> transpose (repeat [])
    * Hangs forever *

sortBy :: (a -> a -> Ordering) -> [a] -> [a] #

The `sortBy` function is the non-overloaded version of `sort`. The argument must be finite.

The supplied comparison relation is supposed to be reflexive and antisymmetric, otherwise, e. g., for `_ _ -> GT`, the ordered list simply does not exist. The relation is also expected to be transitive: if it is not then `sortBy` might fail to find an ordered permutation, even if it exists.

#### Examples

Expand

    >>> sortBy (\(a,_) (b,_) -> compare a b) [(2, "world"), (4, "!"), (1, "Hello")]
    [(1,"Hello"),(2,"world"),(4,"!")]

cycle :: HasCallStack => [a] -> [a] #

`cycle` ties a finite list into a circular one, or equivalently, the infinite repetition of the original list. It is the identity on infinite lists.

#### Examples

Expand

    >>> cycle []
    *** Exception: Prelude.cycle: empty list

    >>> take 10 (cycle [42])
    [42,42,42,42,42,42,42,42,42,42]

    >>> take 10 (cycle [2, 5, 7])
    [2,5,7,2,5,7,2,5,7,2]

    >>> take 1 (cycle (42 : undefined))
    [42]

filter :: (a -> Bool) -> [a] -> [a] #

\(\mathcal{O}(n)\). `filter`, applied to a predicate and a list, returns the list of those elements that satisfy the predicate; i.e.,

    filter p xs = [ x | x <- xs, p x]

#### Examples

Expand

    >>> filter odd [1, 2, 3]
    [1,3]

    >>> filter (\l -> length l > 3) ["Hello", ", ", "World", "!"]
    ["Hello","World"]

    >>> filter (/= 3) [1, 2, 3, 4, 3, 2, 1]
    [1,2,4,2,1]

zip :: [a] -> [b] -> [(a, b)] #

\(\mathcal{O}(\min(m,n))\). `zip` takes two lists and returns a list of corresponding pairs.

`zip` is right-lazy:

    >>> zip [] undefined
    []
    >>> zip undefined []
    *** Exception: Prelude.undefined
    ...

`zip` is capable of list fusion, but it is restricted to its first list argument and its resulting list.

#### Examples

Expand

    >>> zip [1, 2, 3] ['a', 'b', 'c']
    [(1,'a'),(2,'b'),(3,'c')]

If one input list is shorter than the other, excess elements of the longer list are discarded, even if one of the lists is infinite:

    >>> zip [1] ['a', 'b']
    [(1,'a')]

    >>> zip [1, 2] ['a']
    [(1,'a')]

    >>> zip [] [1..]
    []

    >>> zip [1..] []
    []

head :: HasCallStack => [a] -> a #

\(\mathcal{O}(1)\). Extract the first element of a list, which must be non-empty.

To disable the warning about partiality put `{-# OPTIONS_GHC -Wno-x-partial -Wno-unrecognised-warning-flags #-}` at the top of the file. To disable it throughout a package put the same options into `ghc-options` section of Cabal file. To disable it in GHCi put `:set -Wno-x-partial -Wno-unrecognised-warning-flags` into `~/.ghci` config file. See also the migration guide.

##### Examples

Expand

    >>> head [1, 2, 3]
    1

    >>> head [1..]
    1

    >>> head []
    *** Exception: Prelude.head: empty list

uncons :: [a] -> Maybe (a, [a]) #

\(\mathcal{O}(1)\). Decompose a list into its `head` and `tail`.

- If the list is empty, returns `Nothing`.
- If the list is non-empty, returns ``Just` (x, xs)`, where `x` is the `head` of the list and `xs` its `tail`.

@since base-4.8.0.0

#### Examples

Expand

    >>> uncons []
    Nothing

    >>> uncons [1]
    Just (1,[])

    >>> uncons [1, 2, 3]
    Just (1,[2,3])

unsnoc :: [a] -> Maybe ([a], a) #

\(\mathcal{O}(n)\). Decompose a list into `init` and `last`.

- If the list is empty, returns `Nothing`.
- If the list is non-empty, returns ``Just` (xs, x)`, where `xs` is the `init`ial part of the list and `x` is its `last` element.

`unsnoc` is dual to `uncons`: for a finite list `xs`

    unsnoc xs = (\(hd, tl) -> (reverse tl, hd)) <$> uncons (reverse xs)

#### Examples

Expand

    >>> unsnoc []
    Nothing

    >>> unsnoc [1]
    Just ([],1)

    >>> unsnoc [1, 2, 3]
    Just ([1,2],3)

#### Laziness

Expand

    >>> fst <$> unsnoc [undefined]
    Just []

    >>> head . fst <$> unsnoc (1 : undefined)
    Just *** Exception: Prelude.undefined

    >>> head . fst <$> unsnoc (1 : 2 : undefined)
    Just 1

@since base-4.19.0.0

tail :: HasCallStack => [a] -> [a] #

\(\mathcal{O}(1)\). Extract the elements after the head of a list, which must be non-empty.

To disable the warning about partiality put `{-# OPTIONS_GHC -Wno-x-partial -Wno-unrecognised-warning-flags #-}` at the top of the file. To disable it throughout a package put the same options into `ghc-options` section of Cabal file. To disable it in GHCi put `:set -Wno-x-partial -Wno-unrecognised-warning-flags` into `~/.ghci` config file. See also the migration guide.

#### Examples

Expand

    >>> tail [1, 2, 3]
    [2,3]

    >>> tail [1]
    []

    >>> tail []
    *** Exception: Prelude.tail: empty list

last :: HasCallStack => [a] -> a #

\(\mathcal{O}(n)\). Extract the last element of a list, which must be finite and non-empty.

WARNING: This function is partial. Consider using `unsnoc` instead.

#### Examples

Expand

    >>> last [1, 2, 3]
    3

    >>> last [1..]
    * Hangs forever *

    >>> last []
    *** Exception: Prelude.last: empty list

init :: HasCallStack => [a] -> [a] #

\(\mathcal{O}(n)\). Return all the elements of a list except the last one. The list must be non-empty.

WARNING: This function is partial. Consider using `unsnoc` instead.

#### Examples

Expand

    >>> init [1, 2, 3]
    [1,2]

    >>> init [1]
    []

    >>> init []
    *** Exception: Prelude.init: empty list

null :: Foldable t => t a -> Bool #

Test whether the structure is empty. The default implementation is Left-associative and lazy in both the initial element and the accumulator. Thus optimised for structures where the first element can be accessed in constant time. Structures where this is not the case should have a non-default implementation.

#### Examples

Expand

Basic usage:

    >>> null []
    True

    >>> null [1]
    False

`null` is expected to terminate even for infinite structures. The default implementation terminates provided the structure is bounded on the left (there is a leftmost element).

    >>> null [1..]
    False

@since base-4.8.0.0

length :: Foldable t => t a -> Int #

Returns the size/length of a finite structure as an `Int`. The default implementation just counts elements starting with the leftmost. Instances for structures that can compute the element count faster than via element-by-element counting, should provide a specialised implementation.

#### Examples

Expand

Basic usage:

    >>> length []
    0

    >>> length ['a', 'b', 'c']
    3
    >>> length [1..]
    * Hangs forever *

@since base-4.8.0.0

foldl1' :: HasCallStack => (a -> a -> a) -> [a] -> a #

A strict version of `foldl1`.

scanl :: (b -> a -> b) -> b -> [a] -> [b] #

\(\mathcal{O}(n)\). `scanl` is similar to `foldl`, but returns a list of successive reduced values from the left:

    scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]

Note that

    last (scanl f z xs) == foldl f z xs

#### Examples

Expand

    >>> scanl (+) 0 [1..4]
    [0,1,3,6,10]

    >>> scanl (+) 42 []
    [42]

    >>> scanl (-) 100 [1..4]
    [100,99,97,94,90]

    >>> scanl (\reversedString nextChar -> nextChar : reversedString) "foo" ['a', 'b', 'c', 'd']
    ["foo","afoo","bafoo","cbafoo","dcbafoo"]

    >>> take 10 (scanl (+) 0 [1..])
    [0,1,3,6,10,15,21,28,36,45]

    >>> take 1 (scanl undefined 'a' undefined)
    "a"

scanl1 :: (a -> a -> a) -> [a] -> [a] #

\(\mathcal{O}(n)\). `scanl1` is a variant of `scanl` that has no starting value argument:

    scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]

#### Examples

Expand

    >>> scanl1 (+) [1..4]
    [1,3,6,10]

    >>> scanl1 (+) []
    []

    >>> scanl1 (-) [1..4]
    [1,-1,-4,-8]

    >>> scanl1 (&&) [True, False, True, True]
    [True,False,False,False]

    >>> scanl1 (||) [False, False, True, True]
    [False,False,True,True]

    >>> take 10 (scanl1 (+) [1..])
    [1,3,6,10,15,21,28,36,45,55]

    >>> take 1 (scanl1 undefined ('a' : undefined))
    "a"

scanl' :: (b -> a -> b) -> b -> [a] -> [b] #

\(\mathcal{O}(n)\). A strict version of `scanl`.

scanr :: (a -> b -> b) -> b -> [a] -> [b] #

\(\mathcal{O}(n)\). `scanr` is the right-to-left dual of `scanl`. Note that the order of parameters on the accumulating function are reversed compared to `scanl`. Also note that

    head (scanr f z xs) == foldr f z xs.

#### Examples

Expand

    >>> scanr (+) 0 [1..4]
    [10,9,7,4,0]

    >>> scanr (+) 42 []
    [42]

    >>> scanr (-) 100 [1..4]
    [98,-97,99,-96,100]

    >>> scanr (\nextChar reversedString -> nextChar : reversedString) "foo" ['a', 'b', 'c', 'd']
    ["abcdfoo","bcdfoo","cdfoo","dfoo","foo"]

    >>> force $ scanr (+) 0 [1..]
    *** Exception: stack overflow

scanr1 :: (a -> a -> a) -> [a] -> [a] #

\(\mathcal{O}(n)\). `scanr1` is a variant of `scanr` that has no starting value argument.

#### Examples

Expand

    >>> scanr1 (+) [1..4]
    [10,9,7,4]

    >>> scanr1 (+) []
    []

    >>> scanr1 (-) [1..4]
    [-2,3,-1,4]

    >>> scanr1 (&&) [True, False, True, True]
    [False,False,True,True]

    >>> scanr1 (||) [True, True, False, False]
    [True,True,False,False]

    >>> force $ scanr1 (+) [1..]
    *** Exception: stack overflow

iterate :: (a -> a) -> a -> [a] #

`iterate` `f x` returns an infinite list of repeated applications of `f` to `x`:

    iterate f x == [x, f x, f (f x), ...]

#### Laziness

Expand

Note that `iterate` is lazy, potentially leading to thunk build-up if the consumer doesn't force each iterate. See `iterate'` for a strict variant of this function.

    >>> take 1 $ iterate undefined 42
    [42]

#### Examples

Expand

    >>> take 10 $ iterate not True
    [True,False,True,False,True,False,True,False,True,False]

    >>> take 10 $ iterate (+3) 42
    [42,45,48,51,54,57,60,63,66,69]

`iterate id == `repeat``:

    >>> take 10 $ iterate id 1
    [1,1,1,1,1,1,1,1,1,1]

iterate' :: (a -> a) -> a -> [a] #

`iterate'` is the strict version of `iterate`.

It forces the result of each application of the function to weak head normal form (WHNF) before proceeding.

    >>> take 1 $ iterate' undefined 42
    *** Exception: Prelude.undefined

repeat :: a -> [a] #

`repeat` `x` is an infinite list, with `x` the value of every element.

#### Examples

Expand

    >>> take 10 $ repeat 17
    [17,17,17,17,17,17,17,17,17, 17]

    >>> repeat undefined
    [*** Exception: Prelude.undefined

replicate :: Int -> a -> [a] #

`replicate` `n x` is a list of length `n` with `x` the value of every element. It is an instance of the more general `genericReplicate`, in which `n` may be of any integral type.

#### Examples

Expand

    >>> replicate 0 True
    []

    >>> replicate (-1) True
    []

    >>> replicate 4 True
    [True,True,True,True]

takeWhile :: (a -> Bool) -> [a] -> [a] #

`takeWhile`, applied to a predicate `p` and a list `xs`, returns the longest prefix (possibly empty) of `xs` of elements that satisfy `p`.

#### Laziness

Expand

    >>> takeWhile (const False) undefined
    *** Exception: Prelude.undefined

    >>> takeWhile (const False) (undefined : undefined)
    []

    >>> take 1 (takeWhile (const True) (1 : undefined))
    [1]

#### Examples

Expand

    >>> takeWhile (< 3) [1,2,3,4,1,2,3,4]
    [1,2]

    >>> takeWhile (< 9) [1,2,3]
    [1,2,3]

    >>> takeWhile (< 0) [1,2,3]
    []

dropWhile :: (a -> Bool) -> [a] -> [a] #

`dropWhile` `p xs` returns the suffix remaining after `takeWhile` `p xs`.

#### Examples

Expand

    >>> dropWhile (< 3) [1,2,3,4,5,1,2,3]
    [3,4,5,1,2,3]

    >>> dropWhile (< 9) [1,2,3]
    []

    >>> dropWhile (< 0) [1,2,3]
    [1,2,3]

take :: Int -> [a] -> [a] #

`take` `n`, applied to a list `xs`, returns the prefix of `xs` of length `n`, or `xs` itself if `n >= `length` xs`.

It is an instance of the more general `genericTake`, in which `n` may be of any integral type.

#### Laziness

Expand

    >>> take 0 undefined
    []
    >>> take 2 (1 : 2 : undefined)
    [1,2]

#### Examples

Expand

    >>> take 5 "Hello World!"
    "Hello"

    >>> take 3 [1,2,3,4,5]
    [1,2,3]

    >>> take 3 [1,2]
    [1,2]

    >>> take 3 []
    []

    >>> take (-1) [1,2]
    []

    >>> take 0 [1,2]
    []

drop :: Int -> [a] -> [a] #

`drop` `n xs` returns the suffix of `xs` after the first `n` elements, or `[]` if `n >= `length` xs`.

It is an instance of the more general `genericDrop`, in which `n` may be of any integral type.

#### Examples

Expand

    >>> drop 6 "Hello World!"
    "World!"

    >>> drop 3 [1,2,3,4,5]
    [4,5]

    >>> drop 3 [1,2]
    []

    >>> drop 3 []
    []

    >>> drop (-1) [1,2]
    [1,2]

    >>> drop 0 [1,2]
    [1,2]

splitAt :: Int -> [a] -> ([a], [a]) #

`splitAt` `n xs` returns a tuple where first element is `xs` prefix of length `n` and second element is the remainder of the list:

`splitAt` is an instance of the more general `genericSplitAt`, in which `n` may be of any integral type.

#### Laziness

Expand

It is equivalent to `(`take` n xs, `drop` n xs)` unless `n` is `_|_`: `splitAt _|_ xs = _|_`, not `(_|_, _|_)`).

The first component of the tuple is produced lazily:

    >>> fst (splitAt 0 undefined)
    []

    >>> take 1 (fst (splitAt 10 (1 : undefined)))
    [1]

#### Examples

Expand

    >>> splitAt 6 "Hello World!"
    ("Hello ","World!")

    >>> splitAt 3 [1,2,3,4,5]
    ([1,2,3],[4,5])

    >>> splitAt 1 [1,2,3]
    ([1],[2,3])

    >>> splitAt 3 [1,2,3]
    ([1,2,3],[])

    >>> splitAt 4 [1,2,3]
    ([1,2,3],[])

    >>> splitAt 0 [1,2,3]
    ([],[1,2,3])

    >>> splitAt (-1) [1,2,3]
    ([],[1,2,3])

span :: (a -> Bool) -> [a] -> ([a], [a]) #

`span`, applied to a predicate `p` and a list `xs`, returns a tuple where first element is the longest prefix (possibly empty) of `xs` of elements that satisfy `p` and second element is the remainder of the list:

`span` `p xs` is equivalent to `(`takeWhile` p xs, `dropWhile` p xs)`, even if `p` is `_|_`.

#### Laziness

Expand

    >>> span undefined []
    ([],[])
    >>> fst (span (const False) undefined)
    *** Exception: Prelude.undefined
    >>> fst (span (const False) (undefined : undefined))
    []
    >>> take 1 (fst (span (const True) (1 : undefined)))
    [1]

`span` produces the first component of the tuple lazily:

    >>> take 10 (fst (span (const True) [1..]))
    [1,2,3,4,5,6,7,8,9,10]

#### Examples

Expand

    >>> span (< 3) [1,2,3,4,1,2,3,4]
    ([1,2],[3,4,1,2,3,4])

    >>> span (< 9) [1,2,3]
    ([1,2,3],[])

    >>> span (< 0) [1,2,3]
    ([],[1,2,3])

break :: (a -> Bool) -> [a] -> ([a], [a]) #

`break`, applied to a predicate `p` and a list `xs`, returns a tuple where first element is longest prefix (possibly empty) of `xs` of elements that do not satisfy `p` and second element is the remainder of the list:

`break` `p` is equivalent to ``span` (`not` . p)` and consequently to `(`takeWhile` (`not` . p) xs, `dropWhile` (`not` . p) xs)`, even if `p` is `_|_`.

#### Laziness

Expand

    >>> break undefined []
    ([],[])

    >>> fst (break (const True) undefined)
    *** Exception: Prelude.undefined

    >>> fst (break (const True) (undefined : undefined))
    []

    >>> take 1 (fst (break (const False) (1 : undefined)))
    [1]

`break` produces the first component of the tuple lazily:

    >>> take 10 (fst (break (const False) [1..]))
    [1,2,3,4,5,6,7,8,9,10]

#### Examples

Expand

    >>> break (> 3) [1,2,3,4,1,2,3,4]
    ([1,2,3],[4,1,2,3,4])

    >>> break (< 9) [1,2,3]
    ([],[1,2,3])

    >>> break (> 9) [1,2,3]
    ([1,2,3],[])

reverse :: [a] -> [a] #

\(\mathcal{O}(n)\). `reverse` `xs` returns the elements of `xs` in reverse order. `xs` must be finite.

#### Laziness

Expand

`reverse` is lazy in its elements.

    >>> head (reverse [undefined, 1])
    1

    >>> reverse (1 : 2 : undefined)
    *** Exception: Prelude.undefined

#### Examples

Expand

    >>> reverse []
    []

    >>> reverse [42]
    [42]

    >>> reverse [2,5,7]
    [7,5,2]

    >>> reverse [1..]
    * Hangs forever *

and :: Foldable t => t Bool -> Bool #

`and` returns the conjunction of a container of Bools. For the result to be `True`, the container must be finite; `False`, however, results from a `False` value finitely far from the left end.

#### Examples

Expand

Basic usage:

    >>> and []
    True

    >>> and [True]
    True

    >>> and [False]
    False

    >>> and [True, True, False]
    False

    >>> and (False : repeat True) -- Infinite list [False,True,True,True,...
    False

    >>> and (repeat True)
    * Hangs forever *

or :: Foldable t => t Bool -> Bool #

`or` returns the disjunction of a container of Bools. For the result to be `False`, the container must be finite; `True`, however, results from a `True` value finitely far from the left end.

#### Examples

Expand

Basic usage:

    >>> or []
    False

    >>> or [True]
    True

    >>> or [False]
    False

    >>> or [True, True, False]
    True

    >>> or (True : repeat False) -- Infinite list [True,False,False,False,...
    True

    >>> or (repeat False)
    * Hangs forever *

any :: Foldable t => (a -> Bool) -> t a -> Bool #

Determines whether any element of the structure satisfies the predicate.

#### Examples

Expand

Basic usage:

    >>> any (> 3) []
    False

    >>> any (> 3) [1,2]
    False

    >>> any (> 3) [1,2,3,4,5]
    True

    >>> any (> 3) [1..]
    True

    >>> any (> 3) [0, -1..]
    * Hangs forever *

all :: Foldable t => (a -> Bool) -> t a -> Bool #

Determines whether all elements of the structure satisfy the predicate.

#### Examples

Expand

Basic usage:

    >>> all (> 3) []
    True

    >>> all (> 3) [1,2]
    False

    >>> all (> 3) [1,2,3,4,5]
    False

    >>> all (> 3) [1..]
    False

    >>> all (> 3) [4..]
    * Hangs forever *

notElem :: (Foldable t, Eq a) => a -> t a -> Bool infix 4 #

`notElem` is the negation of `elem`.

#### Examples

Expand

Basic usage:

    >>> 3 `notElem` []
    True

    >>> 3 `notElem` [1,2]
    True

    >>> 3 `notElem` [1,2,3,4,5]
    False

For infinite structures, `notElem` terminates if the value exists at a finite distance from the left side of the structure:

    >>> 3 `notElem` [1..]
    False

    >>> 3 `notElem` ([4..] ++ [3])
    * Hangs forever *

lookup :: Eq a => a -> [(a, b)] -> Maybe b #

\(\mathcal{O}(n)\). `lookup` `key assocs` looks up a key in an association list. For the result to be `Nothing`, the list must be finite.

#### Examples

Expand

    >>> lookup 2 []
    Nothing

    >>> lookup 2 [(1, "first")]
    Nothing

    >>> lookup 2 [(1, "first"), (2, "second"), (3, "third")]
    Just "second"

concatMap :: Foldable t => (a -> [b]) -> t a -> [b] #

Map a function over all the elements of a container and concatenate the resulting lists.

#### Examples

Expand

Basic usage:

    >>> concatMap (take 3) [[1..], [10..], [100..], [1000..]]
    [1,2,3,10,11,12,100,101,102,1000,1001,1002]

    >>> concatMap (take 3) (Just [1..])
    [1,2,3]

(!!) :: HasCallStack => [a] -> Int -> a infixl 9 #

List index (subscript) operator, starting from 0. It is an instance of the more general `genericIndex`, which takes an index of any integral type.

WARNING: This function is partial, and should only be used if you are sure that the indexing will not fail. Otherwise, use `!?`.

WARNING: This function takes linear time in the index.

#### Examples

Expand

    >>> ['a', 'b', 'c'] !! 0
    'a'

    >>> ['a', 'b', 'c'] !! 2
    'c'

    >>> ['a', 'b', 'c'] !! 3
    *** Exception: Prelude.!!: index too large

    >>> ['a', 'b', 'c'] !! (-1)
    *** Exception: Prelude.!!: negative index

zip3 :: [a] -> [b] -> [c] -> [(a, b, c)] #

`zip3` takes three lists and returns a list of triples, analogous to `zip`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] #

\(\mathcal{O}(\min(m,n))\). `zipWith` generalises `zip` by zipping with the function given as the first argument, instead of a tupling function.

    zipWith (,) xs ys == zip xs ys
    zipWith f [x1,x2,x3..] [y1,y2,y3..] == [f x1 y1, f x2 y2, f x3 y3..]

`zipWith` is right-lazy:

    >>> let f = undefined
    >>> zipWith f [] undefined
    []

`zipWith` is capable of list fusion, but it is restricted to its first list argument and its resulting list.

#### Examples

Expand

``zipWith` `(+)`` can be applied to two lists to produce the list of corresponding sums:

    >>> zipWith (+) [1, 2, 3] [4, 5, 6]
    [5,7,9]

    >>> zipWith (++) ["hello ", "foo"] ["world!", "bar"]
    ["hello world!","foobar"]

zipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d] #

\(\mathcal{O}(\min(l,m,n))\). The `zipWith3` function takes a function which combines three elements, as well as three lists and returns a list of the function applied to corresponding elements, analogous to `zipWith`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

    zipWith3 (,,) xs ys zs == zip3 xs ys zs
    zipWith3 f [x1,x2,x3..] [y1,y2,y3..] [z1,z2,z3..] == [f x1 y1 z1, f x2 y2 z2, f x3 y3 z3..]

#### Examples

Expand

    >>> zipWith3 (\x y z -> [x, y, z]) "123" "abc" "xyz"
    ["1ax","2by","3cz"]

    >>> zipWith3 (\x y z -> (x * y) + z) [1, 2, 3] [4, 5, 6] [7, 8, 9]
    [11,18,27]

unzip :: [(a, b)] -> ([a], [b]) #

`unzip` transforms a list of pairs into a list of first components and a list of second components.

#### Examples

Expand

    >>> unzip []
    ([],[])

    >>> unzip [(1, 'a'), (2, 'b')]
    ([1,2],"ab")

unzip3 :: [(a, b, c)] -> ([a], [b], [c]) #

The `unzip3` function takes a list of triples and returns three lists of the respective components, analogous to `unzip`.

#### Examples

Expand

    >>> unzip3 []
    ([],[],[])

    >>> unzip3 [(1, 'a', True), (2, 'b', False)]
    ([1,2],"ab",[True,False])

find :: Foldable t => (a -> Bool) -> t a -> Maybe a #

The `find` function takes a predicate and a structure and returns the leftmost element of the structure matching the predicate, or `Nothing` if there is no such element.

#### Examples

Expand

Basic usage:

    >>> find (> 42) [0, 5..]
    Just 45

    >>> find (> 12) [1..7]
    Nothing

dropWhileEnd :: (a -> Bool) -> [a] -> [a] #

The `dropWhileEnd` function drops the largest suffix of a list in which the given predicate holds for all elements.

#### Laziness

Expand

This function is lazy in spine, but strict in elements, which makes it different from `reverse` `.` `dropWhile` `p` `.` `reverse`, which is strict in spine, but lazy in elements. For instance:

    >>> take 1 (dropWhileEnd (< 0) (1 : undefined))
    [1]

    >>> take 1 (reverse $ dropWhile (< 0) $ reverse (1 : undefined))
    *** Exception: Prelude.undefined

but on the other hand

    >>> last (dropWhileEnd (< 0) [undefined, 1])
    *** Exception: Prelude.undefined

    >>> last (reverse $ dropWhile (< 0) $ reverse [undefined, 1])
    1

#### Examples

Expand

    >>> dropWhileEnd isSpace "foo\n"
    "foo"

    >>> dropWhileEnd isSpace "foo bar"
    "foo bar"
    >>> dropWhileEnd (> 10) [1..20]
    [1,2,3,4,5,6,7,8,9,10]

@since base-4.5.0.0

stripPrefix :: Eq a => [a] -> [a] -> Maybe [a] #

\(\mathcal{O}(\min(m,n))\). The `stripPrefix` function drops the given prefix from a list. It returns `Nothing` if the list did not start with the prefix given, or `Just` the list after the prefix, if it does.

##### Examples

Expand

    >>> stripPrefix "foo" "foobar"
    Just "bar"

    >>> stripPrefix "foo" "foo"
    Just ""

    >>> stripPrefix "foo" "barfoo"
    Nothing

    >>> stripPrefix "foo" "barfoobaz"
    Nothing

elemIndex :: Eq a => a -> [a] -> Maybe Int #

The `elemIndex` function returns the index of the first element in the given list which is equal (by `==`) to the query element, or `Nothing` if there is no such element. For the result to be `Nothing`, the list must be finite.

#### Examples

Expand

    >>> elemIndex 4 [0..]
    Just 4

    >>> elemIndex 'o' "haskell"
    Nothing

    >>> elemIndex 0 [1..]
    * hangs forever *

elemIndices :: Eq a => a -> [a] -> [Int] #

The `elemIndices` function extends `elemIndex`, by returning the indices of all elements equal to the query element, in ascending order.

#### Examples

Expand

    >>> elemIndices 'o' "Hello World"
    [4,7]

    >>> elemIndices 1 [1, 2, 3, 1, 2, 3]
    [0,3]

findIndex :: (a -> Bool) -> [a] -> Maybe Int #

The `findIndex` function takes a predicate and a list and returns the index of the first element in the list satisfying the predicate, or `Nothing` if there is no such element. For the result to be `Nothing`, the list must be finite.

#### Examples

Expand

    >>> findIndex isSpace "Hello World!"
    Just 5

    >>> findIndex odd [0, 2, 4, 6]
    Nothing

    >>> findIndex even [1..]
    Just 1

    >>> findIndex odd [0, 2 ..]
    * hangs forever *

findIndices :: (a -> Bool) -> [a] -> [Int] #

The `findIndices` function extends `findIndex`, by returning the indices of all elements satisfying the predicate, in ascending order.

#### Examples

Expand

    >>> findIndices (`elem` "aeiou") "Hello World!"
    [1,4,7]

    >>> findIndices (\l -> length l > 3) ["a", "bcde", "fgh", "ijklmnop"]
    [1,3]

isPrefixOf :: Eq a => [a] -> [a] -> Bool #

\(\mathcal{O}(\min(m,n))\). The `isPrefixOf` function takes two lists and returns `True` iff the first list is a prefix of the second.

#### Examples

Expand

    >>> "Hello" `isPrefixOf` "Hello World!"
    True

    >>> "Hello" `isPrefixOf` "Wello Horld!"
    False

For the result to be `True`, the first list must be finite; `False`, however, results from any mismatch:

    >>> [0..] `isPrefixOf` [1..]
    False

    >>> [0..] `isPrefixOf` [0..99]
    False

    >>> [0..99] `isPrefixOf` [0..]
    True

    >>> [0..] `isPrefixOf` [0..]
    * Hangs forever *

`isPrefixOf` shortcuts when the first argument is empty:

    >>> isPrefixOf [] undefined
    True

isSuffixOf :: Eq a => [a] -> [a] -> Bool #

The `isSuffixOf` function takes two lists and returns `True` iff the first list is a suffix of the second.

#### Examples

Expand

    >>> "ld!" `isSuffixOf` "Hello World!"
    True

    >>> "World" `isSuffixOf` "Hello World!"
    False

The second list must be finite; however the first list may be infinite:

    >>> [0..] `isSuffixOf` [0..99]
    False

    >>> [0..99] `isSuffixOf` [0..]
    * Hangs forever *

isInfixOf :: Eq a => [a] -> [a] -> Bool #

The `isInfixOf` function takes two lists and returns `True` iff the first list is contained, wholly and intact, anywhere within the second.

#### Examples

Expand

    >>> isInfixOf "Haskell" "I really like Haskell."
    True

    >>> isInfixOf "Ial" "I really like Haskell."
    False

For the result to be `True`, the first list must be finite; for the result to be `False`, the second list must be finite:

    >>> [20..50] `isInfixOf` [0..]
    True

    >>> [0..] `isInfixOf` [20..50]
    False

    >>> [0..] `isInfixOf` [0..]
    * Hangs forever *

nub :: Eq a => [a] -> [a] #

\(\mathcal{O}(n^2)\). The `nub` function removes duplicate elements from a list. In particular, it keeps only the first occurrence of each element. (The name `nub` means `essence'.) It is a special case of `nubBy`, which allows the programmer to supply their own equality test.

If there exists `instance Ord a`, it's faster to use `nubOrd` from the `containers` package (link to the latest online documentation), which takes only \(\mathcal{O}(n \log d)\) time where `d` is the number of distinct elements in the list.

Another approach to speed up `nub` is to use `map` `Data.List.NonEmpty.` `head` . `Data.List.NonEmpty.` `group` . `sort`, which takes \(\mathcal{O}(n \log n)\) time, requires `instance Ord a` and doesn't preserve the order.

#### Examples

Expand

    >>> nub [1,2,3,4,3,2,1,2,4,3,5]
    [1,2,3,4,5]

    >>> nub "hello, world!"
    "helo, wrd!"

nubBy :: (a -> a -> Bool) -> [a] -> [a] #

The `nubBy` function behaves just like `nub`, except it uses a user-supplied equality predicate instead of the overloaded `(==)` function.

#### Examples

Expand

    >>> nubBy (\x y -> mod x 3 == mod y 3) [1,2,4,5,6]
    [1,2,6]

    >>> nubBy (/=) [2, 7, 1, 8, 2, 8, 1, 8, 2, 8]
    [2,2,2]

    >>> nubBy (>) [1, 2, 3, 2, 1, 5, 4, 5, 3, 2]
    [1,2,3,5,5]

delete :: Eq a => a -> [a] -> [a] #

\(\mathcal{O}(n)\). `delete` `x` removes the first occurrence of `x` from its list argument.

It is a special case of `deleteBy`, which allows the programmer to supply their own equality test.

#### Examples

Expand

    >>> delete 'a' "banana"
    "bnana"

    >>> delete "not" ["haskell", "is", "not", "awesome"]
    ["haskell","is","awesome"]

deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a] #

\(\mathcal{O}(n)\). The `deleteBy` function behaves like `delete`, but takes a user-supplied equality predicate.

#### Examples

Expand

    >>> deleteBy (<=) 4 [1..10]
    [1,2,3,5,6,7,8,9,10]

    >>> deleteBy (/=) 5 [5, 5, 4, 3, 5, 2]
    [5,5,3,5,2]

(\\) :: Eq a => [a] -> [a] -> [a] infix 5 #

The `\\` function is list difference (non-associative). In the result of `xs` `\\` `ys`, the first occurrence of each element of `ys` in turn (if any) has been removed from `xs`. Thus `(xs ++ ys) \\ xs == ys`.

It is a special case of `deleteFirstsBy`, which allows the programmer to supply their own equality test.

#### Examples

Expand

    >>> "Hello World!" \\ "ell W"
    "Hoorld!"

The second list must be finite, but the first may be infinite.

    >>> take 5 ([0..] \\ [2..4])
    [0,1,5,6,7]

    >>> take 5 ([0..] \\ [2..])
    * Hangs forever *

union :: Eq a => [a] -> [a] -> [a] #

The `union` function returns the list union of the two lists. It is a special case of `unionBy`, which allows the programmer to supply their own equality test.

#### Examples

Expand

    >>> "dog" `union` "cow"
    "dogcw"

If equal elements are present in both lists, an element from the first list will be used. If the second list contains equal elements, only the first one will be retained:

    >>> import Data.Semigroup(Arg(..))
    >>> union [Arg () "dog"] [Arg () "cow"]
    [Arg () "dog"]
    >>> union [] [Arg () "dog", Arg () "cow"]
    [Arg () "dog"]

However if the first list contains duplicates, so will the result:

    >>> "coot" `union` "duck"
    "cootduk"
    >>> "duck" `union` "coot"
    "duckot"

`union` is productive even if both arguments are infinite.

    >>> [0, 2 ..] `union` [1, 3 ..]
    [0,2,4,6,8,10,12..

unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] #

The `unionBy` function is the non-overloaded version of `union`. Both arguments may be infinite.

#### Examples

Expand

    >>> unionBy (>) [3, 4, 5] [1, 2, 3, 4, 5, 6]
    [3,4,5,4,5,6]

    >>> import Data.Semigroup (Arg(..))
    >>> unionBy (/=) [Arg () "Saul"] [Arg () "Kim"]
    [Arg () "Saul", Arg () "Kim"]

intersect :: Eq a => [a] -> [a] -> [a] #

The `intersect` function takes the list intersection of two lists. It is a special case of `intersectBy`, which allows the programmer to supply their own equality test.

##### Examples

Expand

    >>> [1,2,3,4] `intersect` [2,4,6,8]
    [2,4]

If equal elements are present in both lists, an element from the first list will be used, and all duplicates from the second list quashed:

    >>> import Data.Semigroup
    >>> intersect [Arg () "dog"] [Arg () "cow", Arg () "cat"]
    [Arg () "dog"]

However if the first list contains duplicates, so will the result.

    >>> "coot" `intersect` "heron"
    "oo"
    >>> "heron" `intersect` "coot"
    "o"

If the second list is infinite, `intersect` either hangs or returns its first argument in full. Otherwise if the first list is infinite, `intersect` might be productive:

    >>> intersect [100..] [0..]
    [100,101,102,103...
    >>> intersect [0] [1..]
    * Hangs forever *
    >>> intersect [1..] [0]
    * Hangs forever *
    >>> intersect (cycle [1..3]) [2]
    [2,2,2,2...

intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] #

The `intersectBy` function is the non-overloaded version of `intersect`. It is productive for infinite arguments only if the first one is a subset of the second.

intersperse :: a -> [a] -> [a] #

\(\mathcal{O}(n)\). The `intersperse` function takes an element and a list and `intersperses' that element between the elements of the list.

#### Laziness

Expand

`intersperse` has the following properties

    >>> take 1 (intersperse undefined ('a' : undefined))
    "a"

    >>> take 2 (intersperse ',' ('a' : undefined))
    "a*** Exception: Prelude.undefined

#### Examples

Expand

    >>> intersperse ',' "abcde"
    "a,b,c,d,e"

    >>> intersperse 1 [3, 4, 5]
    [3,1,4,1,5]

partition :: (a -> Bool) -> [a] -> ([a], [a]) #

The `partition` function takes a predicate and a list, and returns the pair of lists of elements which do and do not satisfy the predicate, respectively; i.e.,

    partition p xs == (filter p xs, filter (not . p) xs)

#### Examples

Expand

    >>> partition (`elem` "aeiou") "Hello World!"
    ("eoo","Hll Wrld!")

    >>> partition even [1..10]
    ([2,4,6,8,10],[1,3,5,7,9])

    >>> partition (< 5) [1..10]
    ([1,2,3,4],[5,6,7,8,9,10])

insert :: Ord a => a -> [a] -> [a] #

\(\mathcal{O}(n)\). The `insert` function takes an element and a list and inserts the element into the list at the first position where it is less than or equal to the next element. In particular, if the list is sorted before the call, the result will also be sorted. It is a special case of `insertBy`, which allows the programmer to supply their own comparison function.

#### Examples

Expand

    >>> insert (-1) [1, 2, 3]
    [-1,1,2,3]

    >>> insert 'd' "abcefg"
    "abcdefg"

    >>> insert 4 [1, 2, 3, 5, 6, 7]
    [1,2,3,4,5,6,7]

insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a] #

\(\mathcal{O}(n)\). The non-overloaded version of `insert`.

#### Examples

Expand

    >>> insertBy (\x y -> compare (length x) (length y)) [1, 2] [[1], [1, 2, 3], [1, 2, 3, 4]]
    [[1],[1,2],[1,2,3],[1,2,3,4]]

genericLength :: Num i => [a] -> i #

\(\mathcal{O}(n)\). The `genericLength` function is an overloaded version of `length`. In particular, instead of returning an `Int`, it returns any type which is an instance of `Num`. It is, however, less efficient than `length`.

#### Examples

Expand

    >>> genericLength [1, 2, 3] :: Int
    3
    >>> genericLength [1, 2, 3] :: Float
    3.0

Users should take care to pick a return type that is wide enough to contain the full length of the list. If the width is insufficient, the overflow behaviour will depend on the `(+)` implementation in the selected `Num` instance. The following example overflows because the actual list length of 200 lies outside of the `Int8` range of `-128..127`.

    >>> genericLength [1..200] :: Int8
    -56

genericTake :: Integral i => i -> [a] -> [a] #

The `genericTake` function is an overloaded version of `take`, which accepts any `Integral` value as the number of elements to take.

genericDrop :: Integral i => i -> [a] -> [a] #

The `genericDrop` function is an overloaded version of `drop`, which accepts any `Integral` value as the number of elements to drop.

genericSplitAt :: Integral i => i -> [a] -> ([a], [a]) #

The `genericSplitAt` function is an overloaded version of `splitAt`, which accepts any `Integral` value as the position at which to split.

genericIndex :: Integral i => [a] -> i -> a #

The `genericIndex` function is an overloaded version of `!!`, which accepts any `Integral` value as the index.

genericReplicate :: Integral i => i -> a -> [a] #

The `genericReplicate` function is an overloaded version of `replicate`, which accepts any `Integral` value as the number of repetitions to make.

zip4 :: [a] -> [b] -> [c] -> [d] -> [(a, b, c, d)] #

The `zip4` function takes four lists and returns a list of quadruples, analogous to `zip`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a, b, c, d, e)] #

The `zip5` function takes five lists and returns a list of five-tuples, analogous to `zip`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [(a, b, c, d, e, f)] #

The `zip6` function takes six lists and returns a list of six-tuples, analogous to `zip`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [(a, b, c, d, e, f, g)] #

The `zip7` function takes seven lists and returns a list of seven-tuples, analogous to `zip`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

zipWith4 :: (a -> b -> c -> d -> e) -> [a] -> [b] -> [c] -> [d] -> [e] #

The `zipWith4` function takes a function which combines four elements, as well as four lists and returns a list of their point-wise combination, analogous to `zipWith`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

zipWith5 :: (a -> b -> c -> d -> e -> f) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] #

The `zipWith5` function takes a function which combines five elements, as well as five lists and returns a list of their point-wise combination, analogous to `zipWith`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

zipWith6 :: (a -> b -> c -> d -> e -> f -> g) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] #

The `zipWith6` function takes a function which combines six elements, as well as six lists and returns a list of their point-wise combination, analogous to `zipWith`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

zipWith7 :: (a -> b -> c -> d -> e -> f -> g -> h) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [h] #

The `zipWith7` function takes a function which combines seven elements, as well as seven lists and returns a list of their point-wise combination, analogous to `zipWith`. It is capable of list fusion, but it is restricted to its first list argument and its resulting list.

unzip4 :: [(a, b, c, d)] -> ([a], [b], [c], [d]) #

The `unzip4` function takes a list of quadruples and returns four lists, analogous to `unzip`.

unzip5 :: [(a, b, c, d, e)] -> ([a], [b], [c], [d], [e]) #

The `unzip5` function takes a list of five-tuples and returns five lists, analogous to `unzip`.

unzip6 :: [(a, b, c, d, e, f)] -> ([a], [b], [c], [d], [e], [f]) #

The `unzip6` function takes a list of six-tuples and returns six lists, analogous to `unzip`.

unzip7 :: [(a, b, c, d, e, f, g)] -> ([a], [b], [c], [d], [e], [f], [g]) #

The `unzip7` function takes a list of seven-tuples and returns seven lists, analogous to `unzip`.

deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] #

The `deleteFirstsBy` function takes a predicate and two lists and returns the first list with the first occurrence of each element of the second list removed. This is the non-overloaded version of `(\\)`.

    (\\) == deleteFirstsBy (==)

The second list must be finite, but the first may be infinite.

#### Examples

Expand

    >>> deleteFirstsBy (>) [1..10] [3, 4, 5]
    [4,5,6,7,8,9,10]

    >>> deleteFirstsBy (/=) [1..10] [1, 3, 5]
    [4,5,6,7,8,9,10]

group :: Eq a => [a] -> [[a]] #

The `group` function takes a list and returns a list of lists such that the concatenation of the result is equal to the argument. Moreover, each sublist in the result is non-empty, all elements are equal to the first one, and consecutive equal elements of the input end up in the same element of the output list.

`group` is a special case of `groupBy`, which allows the programmer to supply their own equality test.

It's often preferable to use `Data.List.NonEmpty.` `group`, which provides type-level guarantees of non-emptiness of inner lists. A common idiom to squash repeating elements `map` `head` `.` `group` is better served by `map` `Data.List.NonEmpty.` `head` `.` `Data.List.NonEmpty.` `group` because it avoids partial functions.

#### Examples

Expand

    >>> group "Mississippi"
    ["M","i","ss","i","ss","i","pp","i"]

    >>> group [1, 1, 1, 2, 2, 3, 4, 5, 5]
    [[1,1,1],[2,2],[3],[4],[5,5]]

groupBy :: (a -> a -> Bool) -> [a] -> [[a]] #

The `groupBy` function is the non-overloaded version of `group`.

When a supplied relation is not transitive, it is important to remember that equality is checked against the first element in the group, not against the nearest neighbour:

    >>> groupBy (\a b -> b - a < 5) [0..19]
    [[0,1,2,3,4],[5,6,7,8,9],[10,11,12,13,14],[15,16,17,18,19]]

It's often preferable to use `Data.List.NonEmpty.` `groupBy`, which provides type-level guarantees of non-emptiness of inner lists.

#### Examples

Expand

    >>> groupBy (/=) [1, 1, 1, 2, 3, 1, 4, 4, 5]
    [[1],[1],[1,2,3],[1,4,4,5]]

    >>> groupBy (>) [1, 3, 5, 1, 4, 2, 6, 5, 4]
    [[1],[3],[5,1,4,2],[6,5,4]]

    >>> groupBy (const not) [True, False, True, False, False, False, True]
    [[True,False],[True,False,False,False],[True]]

inits :: [a] -> [[a]] #

The `inits` function returns all initial segments of the argument, shortest first.

`inits` is semantically equivalent to ``map` `reverse` . `scanl` (`flip` (:)) []`, but under the hood uses a queue to amortize costs of `reverse`.

#### Laziness

Expand

Note that `inits` has the following strictness property: `inits (xs ++ _|_) = inits xs ++ _|_`

In particular, `inits _|_ = [] : _|_`

#### Examples

Expand

    >>> inits "abc"
    ["","a","ab","abc"]

    >>> inits []
    [[]]

inits is productive on infinite lists:

    >>> take 5 $ inits [1..]
    [[],[1],[1,2],[1,2,3],[1,2,3,4]]

tails :: [a] -> [[a]] #

\(\mathcal{O}(n)\). The `tails` function returns all final segments of the argument, longest first.

#### Laziness

Expand

Note that `tails` has the following strictness property: `tails _|_ = _|_ : _|_`

    >>> tails undefined
    [*** Exception: Prelude.undefined

    >>> drop 1 (tails [undefined, 1, 2])
    [[1, 2], [2], []]

#### Examples

Expand

    >>> tails "abc"
    ["abc","bc","c",""]

    >>> tails [1, 2, 3]
    [[1,2,3],[2,3],[3],[]]

    >>> tails []
    [[]]

subsequences :: [a] -> [[a]] #

The `subsequences` function returns the list of all subsequences of the argument.

#### Laziness

Expand

`subsequences` does not look ahead unless it must:

    >>> take 1 (subsequences undefined)
    [[]]
    >>> take 2 (subsequences ('a' : undefined))
    ["","a"]

#### Examples

Expand

    >>> subsequences "abc"
    ["","a","b","ab","c","ac","bc","abc"]

This function is productive on infinite inputs:

    >>> take 8 $ subsequences ['a'..]
    ["","a","b","ab","c","ac","bc","abc"]

permutations :: [a] -> [[a]] #

The `permutations` function returns the list of all permutations of the argument.

Note that the order of permutations is not lexicographic. It satisfies the following property:

    map (take n) (take (product [1..n]) (permutations ([1..n] ++ undefined))) == permutations [1..n]

#### Laziness

Expand

The `permutations` function is maximally lazy: for each `n`, the value of ``permutations` xs` starts with those permutations that permute ``take` n xs` and keep ``drop` n xs`.

#### Examples

Expand

    >>> permutations "abc"
    ["abc","bac","cba","bca","cab","acb"]

    >>> permutations [1, 2]
    [[1,2],[2,1]]

    >>> permutations []
    [[]]

This function is productive on infinite inputs:

    >>> take 6 $ map (take 3) $ permutations ['a'..]
    ["abc","bac","cba","bca","cab","acb"]

sort :: Ord a => [a] -> [a] #

The `sort` function implements a stable sorting algorithm. It is a special case of `sortBy`, which allows the programmer to supply their own comparison function.

Elements are arranged from lowest to highest, keeping duplicates in the order they appeared in the input.

The argument must be finite.

#### Examples

Expand

    >>> sort [1,6,4,3,2,5]
    [1,2,3,4,5,6]

    >>> sort "haskell"
    "aehklls"

    >>> import Data.Semigroup(Arg(..))
    >>> sort [Arg ":)" 0, Arg ":D" 0, Arg ":)" 1, Arg ":3" 0, Arg ":D" 1]
    [Arg ":)" 0,Arg ":)" 1,Arg ":3" 0,Arg ":D" 0,Arg ":D" 1]

singleton :: a -> [a] #

Construct a list from a single element.

#### Examples

Expand

    >>> singleton True
    [True]

    >>> singleton [1, 2, 3]
    [[1,2,3]]

    >>> singleton 'c'
    "c"

@since base-4.15.0.0

mapAccumL :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b) #

The `mapAccumL` function behaves like a combination of `fmap` and `foldl`; it applies a function to each element of a structure, passing an accumulating parameter from left to right, and returning a final value of this accumulator together with the new structure.

#### Examples

Expand

Basic usage:

    >>> mapAccumL (\a b -> (a + b, a)) 0 [1..10]
    (55,[0,1,3,6,10,15,21,28,36,45])

    >>> mapAccumL (\a b -> (a <> show b, a)) "0" [1..5]
    ("012345",["0","01","012","0123","01234"])

mapAccumR :: Traversable t => (s -> a -> (s, b)) -> s -> t a -> (s, t b) #

The `mapAccumR` function behaves like a combination of `fmap` and `foldr`; it applies a function to each element of a structure, passing an accumulating parameter from right to left, and returning a final value of this accumulator together with the new structure.

#### Examples

Expand

Basic usage:

    >>> mapAccumR (\a b -> (a + b, a)) 0 [1..10]
    (55,[54,52,49,45,40,34,27,19,10,0])

    >>> mapAccumR (\a b -> (a <> show b, a)) "0" [1..5]
    ("054321",["05432","0543","054","05","0"])

isSubsequenceOf :: Eq a => [a] -> [a] -> Bool #

The `isSubsequenceOf` function takes two lists and returns `True` if all the elements of the first list occur, in order, in the second. The elements do not have to occur consecutively.

``isSubsequenceOf` x y` is equivalent to `x ``elem`` (`subsequences` y)`.

Note: `isSubsequenceOf` is often used in infix form.

@since base-4.8.0.0

#### Examples

Expand

    >>> "GHC" `isSubsequenceOf` "The Glorious Haskell Compiler"
    True

    >>> ['a','d'..'z'] `isSubsequenceOf` ['a'..'z']
    True

    >>> [1..10] `isSubsequenceOf` [10,9..0]
    False

For the result to be `True`, the first list must be finite; for the result to be `False`, the second list must be finite:

    >>> [0,2..10] `isSubsequenceOf` [0..]
    True

    >>> [0..] `isSubsequenceOf` [0,2..10]
    False

    >>> [0,2..] `isSubsequenceOf` [0..]
    * Hangs forever*

class Applicative m => Monad (m :: Type -> Type) where #

The `Monad` class defines the basic operations over a monad, a concept from a branch of mathematics known as category theory. From the perspective of a Haskell programmer, however, it is best to think of a monad as an abstract datatype of actions. Haskell's `do` expressions provide a convenient syntax for writing monadic expressions.

Instances of `Monad` should satisfy the following:

Left identity
  ``return` a `>>=` k = k a`
Right identity
  `m `>>=` `return` = m`
Associativity
  `m `>>=` (\x -> k x `>>=` h) = (m `>>=` k) `>>=` h`

Furthermore, the `Monad` and `Applicative` operations should relate as follows:

-     pure = return

-     m1 <*> m2 = m1 >>= (\x1 -> m2 >>= (\x2 -> return (x1 x2)))

The above laws imply:

-     fmap f xs  =  xs >>= return . f

-     (>>) = (*>)

and that `pure` and (`<*>`) satisfy the applicative functor laws.

The instances of `Monad` for `List`, `Maybe` and `IO` defined in the Prelude satisfy these laws.

Minimal complete definition

(>>=)

Methods

(>>=) :: m a -> (a -> m b) -> m b infixl 1 #

Sequentially compose two actions, passing any value produced by the first as an argument to the second.

'`as `>>=` bs`' can be understood as the `do` expression

    do a <- as
       bs a

An alternative name for this function is 'bind', but some people may refer to it as 'flatMap', which results from it being equivialent to

    \x f -> join (fmap f x) :: Monad m => m a -> (a -> m b) -> m b

which can be seen as mapping a value with `Monad m => m a -> m (m b)` and then 'flattening' `m (m b)` to `m b` using `join`.

(>>) :: m a -> m b -> m b infixl 1 #

Sequentially compose two actions, discarding any value produced by the first, like sequencing operators (such as the semicolon) in imperative languages.

'`as `>>` bs`' can be understood as the `do` expression

    do as
       bs

or in terms of ``(>>=)`` as

    as >>= const bs

return :: a -> m a #

Inject a value into the monadic type. This function should not be different from its default implementation as `pure`. The justification for the existence of this function is merely historic.

#### Instances

Instances details

Monad Complex | Since: base-4.9.0.0
Instance details Defined in Data.Complex Methods (>>=) :: Complex a -> (a -> Complex b) -> Complex b # (>>) :: Complex a -> Complex b -> Complex b # return :: a -> Complex a #
Monad First | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods (>>=) :: First a -> (a -> First b) -> First b # (>>) :: First a -> First b -> First b # return :: a -> First a #
Monad Last | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods (>>=) :: Last a -> (a -> Last b) -> Last b # (>>) :: Last a -> Last b -> Last b # return :: a -> Last a #
Monad Max | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods (>>=) :: Max a -> (a -> Max b) -> Max b # (>>) :: Max a -> Max b -> Max b # return :: a -> Max a #
Monad Min | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods (>>=) :: Min a -> (a -> Min b) -> Min b # (>>) :: Min a -> Min b -> Min b # return :: a -> Min a #
Monad Put |
Instance details Defined in Data.ByteString.Builder.Internal Methods (>>=) :: Put a -> (a -> Put b) -> Put b # (>>) :: Put a -> Put b -> Put b # return :: a -> Put a #
Monad Seq |
Instance details Defined in Data.Sequence.Internal Methods (>>=) :: Seq a -> (a -> Seq b) -> Seq b # (>>) :: Seq a -> Seq b -> Seq b # return :: a -> Seq a #
Monad Tree |
Instance details Defined in Data.Tree Methods (>>=) :: Tree a -> (a -> Tree b) -> Tree b # (>>) :: Tree a -> Tree b -> Tree b # return :: a -> Tree a #
Monad NonEmpty | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods (>>=) :: NonEmpty a -> (a -> NonEmpty b) -> NonEmpty b # (>>) :: NonEmpty a -> NonEmpty b -> NonEmpty b # return :: a -> NonEmpty a #
Monad Down | @since base-4.11.0.0
Instance details Defined in GHC.Internal.Data.Ord Methods (>>=) :: Down a -> (a -> Down b) -> Down b # (>>) :: Down a -> Down b -> Down b # return :: a -> Down a #
Monad Par1 | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods (>>=) :: Par1 a -> (a -> Par1 b) -> Par1 b # (>>) :: Par1 a -> Par1 b -> Par1 b # return :: a -> Par1 a #
Monad P | @since base-2.01
Instance details Defined in GHC.Internal.Text.ParserCombinators.ReadP Methods (>>=) :: P a -> (a -> P b) -> P b # (>>) :: P a -> P b -> P b # return :: a -> P a #
Monad ReadP | @since base-2.01
Instance details Defined in GHC.Internal.Text.ParserCombinators.ReadP Methods (>>=) :: ReadP a -> (a -> ReadP b) -> ReadP b # (>>) :: ReadP a -> ReadP b -> ReadP b # return :: a -> ReadP a #
Monad IO | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods (>>=) :: IO a -> (a -> IO b) -> IO b # (>>) :: IO a -> IO b -> IO b # return :: a -> IO a #
Monad Array |
Instance details Defined in Data.Primitive.Array Methods (>>=) :: Array a -> (a -> Array b) -> Array b # (>>) :: Array a -> Array b -> Array b # return :: a -> Array a #
Monad SmallArray |
Instance details Defined in Data.Primitive.SmallArray Methods (>>=) :: SmallArray a -> (a -> SmallArray b) -> SmallArray b # (>>) :: SmallArray a -> SmallArray b -> SmallArray b # return :: a -> SmallArray a #
Monad Vector |
Instance details Defined in Data.Vector Methods (>>=) :: Vector a -> (a -> Vector b) -> Vector b # (>>) :: Vector a -> Vector b -> Vector b # return :: a -> Vector a #
Monad Id |
Instance details Defined in Data.Vector.Fusion.Util Methods (>>=) :: Id a -> (a -> Id b) -> Id b # (>>) :: Id a -> Id b -> Id b # return :: a -> Id a #
Monad Vector |
Instance details Defined in Data.Vector.Strict Methods (>>=) :: Vector a -> (a -> Vector b) -> Vector b # (>>) :: Vector a -> Vector b -> Vector b # return :: a -> Vector a #
Monad Maybe | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods (>>=) :: Maybe a -> (a -> Maybe b) -> Maybe b # (>>) :: Maybe a -> Maybe b -> Maybe b # return :: a -> Maybe a #
Monad Solo | @since base-4.15
Instance details Defined in GHC.Internal.Base Methods (>>=) :: Solo a -> (a -> Solo b) -> Solo b # (>>) :: Solo a -> Solo b -> Solo b # return :: a -> Solo a #
Monad [] | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods (>>=) :: [a] -> (a -> [b]) -> [b] # (>>) :: [a] -> [b] -> [b] # return :: a -> [a] #
Monad m => Monad (WrappedMonad m) | Since: base-4.7.0.0
Instance details Defined in Control.Applicative Methods (>>=) :: WrappedMonad m a -> (a -> WrappedMonad m b) -> WrappedMonad m b # (>>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b # return :: a -> WrappedMonad m a #
Monad (SetM s) |
Instance details Defined in Data.Graph Methods (>>=) :: SetM s a -> (a -> SetM s b) -> SetM s b # (>>) :: SetM s a -> SetM s b -> SetM s b # return :: a -> SetM s a #
ArrowApply a => Monad (ArrowMonad a) | @since base-2.01
Instance details Defined in GHC.Internal.Control.Arrow Methods (>>=) :: ArrowMonad a a0 -> (a0 -> ArrowMonad a b) -> ArrowMonad a b # (>>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b # return :: a0 -> ArrowMonad a a0 #
Monad (Either e) | @since base-4.4.0.0
Instance details Defined in GHC.Internal.Data.Either Methods (>>=) :: Either e a -> (a -> Either e b) -> Either e b # (>>) :: Either e a -> Either e b -> Either e b # return :: a -> Either e a #
Monad (U1 :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods (>>=) :: U1 a -> (a -> U1 b) -> U1 b # (>>) :: U1 a -> U1 b -> U1 b # return :: a -> U1 a #
Monad (IParser t) |
Instance details Defined in Data.Text.Internal.Read Methods (>>=) :: IParser t a -> (a -> IParser t b) -> IParser t b # (>>) :: IParser t a -> IParser t b -> IParser t b # return :: a -> IParser t a #
Monad m => Monad (MaybeT m) |
Instance details Defined in Control.Monad.Trans.Maybe Methods (>>=) :: MaybeT m a -> (a -> MaybeT m b) -> MaybeT m b # (>>) :: MaybeT m a -> MaybeT m b -> MaybeT m b # return :: a -> MaybeT m a #
Monoid a => Monad ((,) a) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods (>>=) :: (a, a0) -> (a0 -> (a, b)) -> (a, b) # (>>) :: (a, a0) -> (a, b) -> (a, b) # return :: a0 -> (a, a0) #
(Applicative f, Monad f) => Monad (WhenMissing f x) | Equivalent to `ReaderT k (ReaderT x (MaybeT f))`. Since: containers-0.5.9
Instance details Defined in Data.IntMap.Internal Methods (>>=) :: WhenMissing f x a -> (a -> WhenMissing f x b) -> WhenMissing f x b # (>>) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x b # return :: a -> WhenMissing f x a #
Monad m => Monad (Kleisli m a) | @since base-4.14.0.0
Instance details Defined in GHC.Internal.Control.Arrow Methods (>>=) :: Kleisli m a a0 -> (a0 -> Kleisli m a b) -> Kleisli m a b # (>>) :: Kleisli m a a0 -> Kleisli m a b -> Kleisli m a b # return :: a0 -> Kleisli m a a0 #
Monad f => Monad (Rec1 f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods (>>=) :: Rec1 f a -> (a -> Rec1 f b) -> Rec1 f b # (>>) :: Rec1 f a -> Rec1 f b -> Rec1 f b # return :: a -> Rec1 f a #
(Monoid w, Functor m, Monad m) => Monad (AccumT w m) |
Instance details Defined in Control.Monad.Trans.Accum Methods (>>=) :: AccumT w m a -> (a -> AccumT w m b) -> AccumT w m b # (>>) :: AccumT w m a -> AccumT w m b -> AccumT w m b # return :: a -> AccumT w m a #
Monad m => Monad (ExceptT e m) |
Instance details Defined in Control.Monad.Trans.Except Methods (>>=) :: ExceptT e m a -> (a -> ExceptT e m b) -> ExceptT e m b # (>>) :: ExceptT e m a -> ExceptT e m b -> ExceptT e m b # return :: a -> ExceptT e m a #
Monad m => Monad (IdentityT m) |
Instance details Defined in Control.Monad.Trans.Identity Methods (>>=) :: IdentityT m a -> (a -> IdentityT m b) -> IdentityT m b # (>>) :: IdentityT m a -> IdentityT m b -> IdentityT m b # return :: a -> IdentityT m a #
Monad m => Monad (ReaderT r m) |
Instance details Defined in Control.Monad.Trans.Reader Methods (>>=) :: ReaderT r m a -> (a -> ReaderT r m b) -> ReaderT r m b # (>>) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m b # return :: a -> ReaderT r m a #
Monad m => Monad (SelectT r m) |
Instance details Defined in Control.Monad.Trans.Select Methods (>>=) :: SelectT r m a -> (a -> SelectT r m b) -> SelectT r m b # (>>) :: SelectT r m a -> SelectT r m b -> SelectT r m b # return :: a -> SelectT r m a #
Monad m => Monad (StateT s m) |
Instance details Defined in Control.Monad.Trans.State.Lazy Methods (>>=) :: StateT s m a -> (a -> StateT s m b) -> StateT s m b # (>>) :: StateT s m a -> StateT s m b -> StateT s m b # return :: a -> StateT s m a #
Monad m => Monad (StateT s m) |
Instance details Defined in Control.Monad.Trans.State.Strict Methods (>>=) :: StateT s m a -> (a -> StateT s m b) -> StateT s m b # (>>) :: StateT s m a -> StateT s m b -> StateT s m b # return :: a -> StateT s m a #
Monad m => Monad (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.CPS Methods (>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b # (>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b # return :: a -> WriterT w m a #
(Monoid w, Monad m) => Monad (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods (>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b # (>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b # return :: a -> WriterT w m a #
(Monoid w, Monad m) => Monad (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods (>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b # (>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b # return :: a -> WriterT w m a #
Monad m => Monad (Reverse m) | Derived instance.
Instance details Defined in Data.Functor.Reverse Methods (>>=) :: Reverse m a -> (a -> Reverse m b) -> Reverse m b # (>>) :: Reverse m a -> Reverse m b -> Reverse m b # return :: a -> Reverse m a #
(Monoid a, Monoid b) => Monad ((,,) a b) | @since base-4.14.0.0
Instance details Defined in GHC.Internal.Base Methods (>>=) :: (a, b, a0) -> (a0 -> (a, b, b0)) -> (a, b, b0) # (>>) :: (a, b, a0) -> (a, b, b0) -> (a, b, b0) # return :: a0 -> (a, b, a0) #
(Monad f, Monad g) => Monad (Product f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Product Methods (>>=) :: Product f g a -> (a -> Product f g b) -> Product f g b # (>>) :: Product f g a -> Product f g b -> Product f g b # return :: a -> Product f g a #
(Monad f, Applicative f) => Monad (WhenMatched f x y) | Equivalent to `ReaderT Key (ReaderT x (ReaderT y (MaybeT f)))` Since: containers-0.5.9
Instance details Defined in Data.IntMap.Internal Methods (>>=) :: WhenMatched f x y a -> (a -> WhenMatched f x y b) -> WhenMatched f x y b # (>>) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y b # return :: a -> WhenMatched f x y a #
(Applicative f, Monad f) => Monad (WhenMissing f k x) | Equivalent to `ReaderT k (ReaderT x (MaybeT f))` . Since: containers-0.5.9
Instance details Defined in Data.Map.Internal Methods (>>=) :: WhenMissing f k x a -> (a -> WhenMissing f k x b) -> WhenMissing f k x b # (>>) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x b # return :: a -> WhenMissing f k x a #
(Monad f, Monad g) => Monad (f :*: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods (>>=) :: (f :*: g) a -> (a -> (f :*: g) b) -> (f :*: g) b # (>>) :: (f :*: g) a -> (f :*: g) b -> (f :*: g) b # return :: a -> (f :*: g) a #
Monad (ContT r m) |
Instance details Defined in Control.Monad.Trans.Cont Methods (>>=) :: ContT r m a -> (a -> ContT r m b) -> ContT r m b # (>>) :: ContT r m a -> ContT r m b -> ContT r m b # return :: a -> ContT r m a #
(Monoid a, Monoid b, Monoid c) => Monad ((,,,) a b c) | @since base-4.14.0.0
Instance details Defined in GHC.Internal.Base Methods (>>=) :: (a, b, c, a0) -> (a0 -> (a, b, c, b0)) -> (a, b, c, b0) # (>>) :: (a, b, c, a0) -> (a, b, c, b0) -> (a, b, c, b0) # return :: a0 -> (a, b, c, a0) #
Monad ((->) r) | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods (>>=) :: (r -> a) -> (a -> r -> b) -> r -> b # (>>) :: (r -> a) -> (r -> b) -> r -> b # return :: a -> r -> a #
(Monad f, Applicative f) => Monad (WhenMatched f k x y) | Equivalent to `ReaderT k (ReaderT x (ReaderT y (MaybeT f)))` Since: containers-0.5.9
Instance details Defined in Data.Map.Internal Methods (>>=) :: WhenMatched f k x y a -> (a -> WhenMatched f k x y b) -> WhenMatched f k x y b # (>>) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y b # return :: a -> WhenMatched f k x y a #
Monad f => Monad (M1 i c f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods (>>=) :: M1 i c f a -> (a -> M1 i c f b) -> M1 i c f b # (>>) :: M1 i c f a -> M1 i c f b -> M1 i c f b # return :: a -> M1 i c f a #
Monad m => Monad (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.CPS Methods (>>=) :: RWST r w s m a -> (a -> RWST r w s m b) -> RWST r w s m b # (>>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b # return :: a -> RWST r w s m a #
(Monoid w, Monad m) => Monad (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.Lazy Methods (>>=) :: RWST r w s m a -> (a -> RWST r w s m b) -> RWST r w s m b # (>>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b # return :: a -> RWST r w s m a #
(Monoid w, Monad m) => Monad (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.Strict Methods (>>=) :: RWST r w s m a -> (a -> RWST r w s m b) -> RWST r w s m b # (>>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b # return :: a -> RWST r w s m a #

class Functor (f :: Type -> Type) where #

A type `f` is a Functor if it provides a function `fmap` which, given any types `a` and `b` lets you apply any function from `(a -> b)` to turn an `f a` into an `f b`, preserving the structure of `f`. Furthermore `f` needs to adhere to the following:

Identity
  ``fmap` `id` == `id``
Composition
  ``fmap` (f . g) == `fmap` f . `fmap` g`

Note, that the second law follows from the free theorem of the type `fmap` and the first law, so you need only check that the former condition holds. See these articles by School of Haskell or David Luposchainsky for an explanation.

Minimal complete definition

fmap

Methods

fmap :: (a -> b) -> f a -> f b #

`fmap` is used to apply a function of type `(a -> b)` to a value of type `f a`, where f is a functor, to produce a value of type `f b`. Note that for any type constructor with more than one parameter (e.g., `Either`), only the last type parameter can be modified with `fmap` (e.g., `b` in `Either a b`).

Some type constructors with two parameters or more have a ``Bifunctor`` instance that allows both the last and the penultimate parameters to be mapped over.

#### Examples

Expand

Convert from a ``Maybe` Int` to a `Maybe String` using `show`:

    >>> fmap show Nothing
    Nothing
    >>> fmap show (Just 3)
    Just "3"

Convert from an ``Either` Int Int` to an `Either Int String` using `show`:

    >>> fmap show (Left 17)
    Left 17
    >>> fmap show (Right 17)
    Right "17"

Double each element of a list:

    >>> fmap (*2) [1,2,3]
    [2,4,6]

Apply `even` to the second element of a pair:

    >>> fmap even (2,2)
    (2,True)

It may seem surprising that the function is only applied to the last element of the tuple compared to the list example above which applies it to every element in the list. To understand, remember that tuples are type constructors with multiple type parameters: a tuple of 3 elements `(a,b,c)` can also be written `(,,) a b c` and its `Functor` instance is defined for `Functor ((,,) a b)` (i.e., only the third parameter is free to be mapped over with `fmap`).

It explains why `fmap` can be used with tuples containing values of different types as in the following example:

    >>> fmap even ("hello", 1.0, 4)
    ("hello",1.0,True)

(<$) :: a -> f b -> f a infixl 4 #

Replace all locations in the input with the same value. The default definition is ``fmap` . `const``, but this may be overridden with a more efficient version.

#### Examples

Expand

Perform a computation with `Maybe` and replace the result with a constant value if it is `Just`:

    >>> 'a' <$ Just 2
    Just 'a'
    >>> 'a' <$ Nothing
    Nothing

#### Instances

Instances details

Functor Complex | Since: base-4.9.0.0
Instance details Defined in Data.Complex Methods fmap :: (a -> b) -> Complex a -> Complex b # (<$) :: a -> Complex b -> Complex a #
Functor First | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fmap :: (a -> b) -> First a -> First b # (<$) :: a -> First b -> First a #
Functor Last | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fmap :: (a -> b) -> Last a -> Last b # (<$) :: a -> Last b -> Last a #
Functor Max | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fmap :: (a -> b) -> Max a -> Max b # (<$) :: a -> Max b -> Max a #
Functor Min | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fmap :: (a -> b) -> Min a -> Min b # (<$) :: a -> Min b -> Min a #
Functor ArgDescr | Since: base-4.7.0.0
Instance details Defined in System.Console.GetOpt Methods fmap :: (a -> b) -> ArgDescr a -> ArgDescr b # (<$) :: a -> ArgDescr b -> ArgDescr a #
Functor ArgOrder | Since: base-4.7.0.0
Instance details Defined in System.Console.GetOpt Methods fmap :: (a -> b) -> ArgOrder a -> ArgOrder b # (<$) :: a -> ArgOrder b -> ArgOrder a #
Functor OptDescr | Since: base-4.7.0.0
Instance details Defined in System.Console.GetOpt Methods fmap :: (a -> b) -> OptDescr a -> OptDescr b # (<$) :: a -> OptDescr b -> OptDescr a #
Functor Put |
Instance details Defined in Data.ByteString.Builder.Internal Methods fmap :: (a -> b) -> Put a -> Put b # (<$) :: a -> Put b -> Put a #
Functor SCC | Since: containers-0.5.4
Instance details Defined in Data.Graph Methods fmap :: (a -> b) -> SCC a -> SCC b # (<$) :: a -> SCC b -> SCC a #
Functor IntMap |
Instance details Defined in Data.IntMap.Internal Methods fmap :: (a -> b) -> IntMap a -> IntMap b # (<$) :: a -> IntMap b -> IntMap a #
Functor Digit |
Instance details Defined in Data.Sequence.Internal Methods fmap :: (a -> b) -> Digit a -> Digit b # (<$) :: a -> Digit b -> Digit a #
Functor Elem |
Instance details Defined in Data.Sequence.Internal Methods fmap :: (a -> b) -> Elem a -> Elem b # (<$) :: a -> Elem b -> Elem a #
Functor FingerTree |
Instance details Defined in Data.Sequence.Internal Methods fmap :: (a -> b) -> FingerTree a -> FingerTree b # (<$) :: a -> FingerTree b -> FingerTree a #
Functor Node |
Instance details Defined in Data.Sequence.Internal Methods fmap :: (a -> b) -> Node a -> Node b # (<$) :: a -> Node b -> Node a #
Functor Seq |
Instance details Defined in Data.Sequence.Internal Methods fmap :: (a -> b) -> Seq a -> Seq b # (<$) :: a -> Seq b -> Seq a #
Functor ViewL |
Instance details Defined in Data.Sequence.Internal Methods fmap :: (a -> b) -> ViewL a -> ViewL b # (<$) :: a -> ViewL b -> ViewL a #
Functor ViewR |
Instance details Defined in Data.Sequence.Internal Methods fmap :: (a -> b) -> ViewR a -> ViewR b # (<$) :: a -> ViewR b -> ViewR a #
Functor Tree |
Instance details Defined in Data.Tree Methods fmap :: (a -> b) -> Tree a -> Tree b # (<$) :: a -> Tree b -> Tree a #
Functor NonEmpty | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> NonEmpty a -> NonEmpty b # (<$) :: a -> NonEmpty b -> NonEmpty a #
Functor Down | @since base-4.11.0.0
Instance details Defined in GHC.Internal.Data.Ord Methods fmap :: (a -> b) -> Down a -> Down b # (<$) :: a -> Down b -> Down a #
Functor Par1 | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> Par1 a -> Par1 b # (<$) :: a -> Par1 b -> Par1 a #
Functor P | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Text.ParserCombinators.ReadP Methods fmap :: (a -> b) -> P a -> P b # (<$) :: a -> P b -> P a #
Functor ReadP | @since base-2.01
Instance details Defined in GHC.Internal.Text.ParserCombinators.ReadP Methods fmap :: (a -> b) -> ReadP a -> ReadP b # (<$) :: a -> ReadP b -> ReadP a #
Functor IO | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> IO a -> IO b # (<$) :: a -> IO b -> IO a #
Functor AnnotDetails |
Instance details Defined in Text.PrettyPrint.Annotated.HughesPJ Methods fmap :: (a -> b) -> AnnotDetails a -> AnnotDetails b # (<$) :: a -> AnnotDetails b -> AnnotDetails a #
Functor Doc |
Instance details Defined in Text.PrettyPrint.Annotated.HughesPJ Methods fmap :: (a -> b) -> Doc a -> Doc b # (<$) :: a -> Doc b -> Doc a #
Functor Span |
Instance details Defined in Text.PrettyPrint.Annotated.HughesPJ Methods fmap :: (a -> b) -> Span a -> Span b # (<$) :: a -> Span b -> Span a #
Functor Array |
Instance details Defined in Data.Primitive.Array Methods fmap :: (a -> b) -> Array a -> Array b # (<$) :: a -> Array b -> Array a #
Functor SmallArray |
Instance details Defined in Data.Primitive.SmallArray Methods fmap :: (a -> b) -> SmallArray a -> SmallArray b # (<$) :: a -> SmallArray b -> SmallArray a #
Functor Vector |
Instance details Defined in Data.Vector Methods fmap :: (a -> b) -> Vector a -> Vector b # (<$) :: a -> Vector b -> Vector a #
Functor Id |
Instance details Defined in Data.Vector.Fusion.Util Methods fmap :: (a -> b) -> Id a -> Id b # (<$) :: a -> Id b -> Id a #
Functor Vector |
Instance details Defined in Data.Vector.Strict Methods fmap :: (a -> b) -> Vector a -> Vector b # (<$) :: a -> Vector b -> Vector a #
Functor Maybe | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> Maybe a -> Maybe b # (<$) :: a -> Maybe b -> Maybe a #
Functor Solo | @since base-4.15
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> Solo a -> Solo b # (<$) :: a -> Solo b -> Solo a #
Functor [] | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> [a] -> [b] # (<$) :: a -> [b] -> [a] #
Monad m => Functor (WrappedMonad m) | Since: base-2.1
Instance details Defined in Control.Applicative Methods fmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b # (<$) :: a -> WrappedMonad m b -> WrappedMonad m a #
Functor (Arg a) | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fmap :: (a0 -> b) -> Arg a a0 -> Arg a b # (<$) :: a0 -> Arg a b -> Arg a a0 #
Functor (SetM s) |
Instance details Defined in Data.Graph Methods fmap :: (a -> b) -> SetM s a -> SetM s b # (<$) :: a -> SetM s b -> SetM s a #
Functor (Map k) |
Instance details Defined in Data.Map.Internal Methods fmap :: (a -> b) -> Map k a -> Map k b # (<$) :: a -> Map k b -> Map k a #
Arrow a => Functor (ArrowMonad a) | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Control.Arrow Methods fmap :: (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b # (<$) :: a0 -> ArrowMonad a b -> ArrowMonad a a0 #
Functor (Either a) | @since base-3.0
Instance details Defined in GHC.Internal.Data.Either Methods fmap :: (a0 -> b) -> Either a a0 -> Either a b # (<$) :: a0 -> Either a b -> Either a a0 #
Functor (U1 :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> U1 a -> U1 b # (<$) :: a -> U1 b -> U1 a #
Functor (V1 :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> V1 a -> V1 b # (<$) :: a -> V1 b -> V1 a #
Functor (IParser t) |
Instance details Defined in Data.Text.Internal.Read Methods fmap :: (a -> b) -> IParser t a -> IParser t b # (<$) :: a -> IParser t b -> IParser t a #
Functor f => Functor (Lift f) |
Instance details Defined in Control.Applicative.Lift Methods fmap :: (a -> b) -> Lift f a -> Lift f b # (<$) :: a -> Lift f b -> Lift f a #
Functor m => Functor (MaybeT m) |
Instance details Defined in Control.Monad.Trans.Maybe Methods fmap :: (a -> b) -> MaybeT m a -> MaybeT m b # (<$) :: a -> MaybeT m b -> MaybeT m a #
Functor (HashMap k) |
Instance details Defined in Data.HashMap.Internal Methods fmap :: (a -> b) -> HashMap k a -> HashMap k b # (<$) :: a -> HashMap k b -> HashMap k a #
Functor ((,) a) | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods fmap :: (a0 -> b) -> (a, a0) -> (a, b) # (<$) :: a0 -> (a, b) -> (a, a0) #
Arrow a => Functor (WrappedArrow a b) | Since: base-2.1
Instance details Defined in Control.Applicative Methods fmap :: (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 # (<$) :: a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 #
(Applicative f, Monad f) => Functor (WhenMissing f x) | Since: containers-0.5.9
Instance details Defined in Data.IntMap.Internal Methods fmap :: (a -> b) -> WhenMissing f x a -> WhenMissing f x b # (<$) :: a -> WhenMissing f x b -> WhenMissing f x a #
Functor m => Functor (Kleisli m a) | @since base-4.14.0.0
Instance details Defined in GHC.Internal.Control.Arrow Methods fmap :: (a0 -> b) -> Kleisli m a a0 -> Kleisli m a b # (<$) :: a0 -> Kleisli m a b -> Kleisli m a a0 #
(Generic1 f, Functor (Rep1 f)) => Functor (Generically1 f) | @since base-4.17.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> Generically1 f a -> Generically1 f b # (<$) :: a -> Generically1 f b -> Generically1 f a #
Functor f => Functor (Rec1 f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> Rec1 f a -> Rec1 f b # (<$) :: a -> Rec1 f b -> Rec1 f a #
Functor (URec (Ptr ()) :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec (Ptr ()) a -> URec (Ptr ()) b # (<$) :: a -> URec (Ptr ()) b -> URec (Ptr ()) a #
Functor (URec Char :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Char a -> URec Char b # (<$) :: a -> URec Char b -> URec Char a #
Functor (URec Double :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Double a -> URec Double b # (<$) :: a -> URec Double b -> URec Double a #
Functor (URec Float :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Float a -> URec Float b # (<$) :: a -> URec Float b -> URec Float a #
Functor (URec Int :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Int a -> URec Int b # (<$) :: a -> URec Int b -> URec Int a #
Functor (URec Word :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Word a -> URec Word b # (<$) :: a -> URec Word b -> URec Word a #
Functor f => Functor (Backwards f) | Derived instance.
Instance details Defined in Control.Applicative.Backwards Methods fmap :: (a -> b) -> Backwards f a -> Backwards f b # (<$) :: a -> Backwards f b -> Backwards f a #
Functor m => Functor (AccumT w m) |
Instance details Defined in Control.Monad.Trans.Accum Methods fmap :: (a -> b) -> AccumT w m a -> AccumT w m b # (<$) :: a -> AccumT w m b -> AccumT w m a #
Functor m => Functor (ExceptT e m) |
Instance details Defined in Control.Monad.Trans.Except Methods fmap :: (a -> b) -> ExceptT e m a -> ExceptT e m b # (<$) :: a -> ExceptT e m b -> ExceptT e m a #
Functor m => Functor (IdentityT m) |
Instance details Defined in Control.Monad.Trans.Identity Methods fmap :: (a -> b) -> IdentityT m a -> IdentityT m b # (<$) :: a -> IdentityT m b -> IdentityT m a #
Functor m => Functor (ReaderT r m) |
Instance details Defined in Control.Monad.Trans.Reader Methods fmap :: (a -> b) -> ReaderT r m a -> ReaderT r m b # (<$) :: a -> ReaderT r m b -> ReaderT r m a #
Functor m => Functor (SelectT r m) |
Instance details Defined in Control.Monad.Trans.Select Methods fmap :: (a -> b) -> SelectT r m a -> SelectT r m b # (<$) :: a -> SelectT r m b -> SelectT r m a #
Functor m => Functor (StateT s m) |
Instance details Defined in Control.Monad.Trans.State.Lazy Methods fmap :: (a -> b) -> StateT s m a -> StateT s m b # (<$) :: a -> StateT s m b -> StateT s m a #
Functor m => Functor (StateT s m) |
Instance details Defined in Control.Monad.Trans.State.Strict Methods fmap :: (a -> b) -> StateT s m a -> StateT s m b # (<$) :: a -> StateT s m b -> StateT s m a #
Functor m => Functor (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.CPS Methods fmap :: (a -> b) -> WriterT w m a -> WriterT w m b # (<$) :: a -> WriterT w m b -> WriterT w m a #
Functor m => Functor (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods fmap :: (a -> b) -> WriterT w m a -> WriterT w m b # (<$) :: a -> WriterT w m b -> WriterT w m a #
Functor m => Functor (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods fmap :: (a -> b) -> WriterT w m a -> WriterT w m b # (<$) :: a -> WriterT w m b -> WriterT w m a #
Functor (Constant a :: Type -> Type) |
Instance details Defined in Data.Functor.Constant Methods fmap :: (a0 -> b) -> Constant a a0 -> Constant a b # (<$) :: a0 -> Constant a b -> Constant a a0 #
Functor f => Functor (Reverse f) | Derived instance.
Instance details Defined in Data.Functor.Reverse Methods fmap :: (a -> b) -> Reverse f a -> Reverse f b # (<$) :: a -> Reverse f b -> Reverse f a #
Monad m => Functor (Bundle m v) |
Instance details Defined in Data.Vector.Fusion.Bundle.Monadic Methods fmap :: (a -> b) -> Bundle m v a -> Bundle m v b # (<$) :: a -> Bundle m v b -> Bundle m v a #
Functor ((,,) a b) | @since base-4.14.0.0
Instance details Defined in GHC.Internal.Base Methods fmap :: (a0 -> b0) -> (a, b, a0) -> (a, b, b0) # (<$) :: a0 -> (a, b, b0) -> (a, b, a0) #
(Functor f, Functor g) => Functor (Product f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Product Methods fmap :: (a -> b) -> Product f g a -> Product f g b # (<$) :: a -> Product f g b -> Product f g a #
(Functor f, Functor g) => Functor (Sum f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Sum Methods fmap :: (a -> b) -> Sum f g a -> Sum f g b # (<$) :: a -> Sum f g b -> Sum f g a #
Functor f => Functor (WhenMatched f x y) | Since: containers-0.5.9
Instance details Defined in Data.IntMap.Internal Methods fmap :: (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b # (<$) :: a -> WhenMatched f x y b -> WhenMatched f x y a #
(Applicative f, Monad f) => Functor (WhenMissing f k x) | Since: containers-0.5.9
Instance details Defined in Data.Map.Internal Methods fmap :: (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b # (<$) :: a -> WhenMissing f k x b -> WhenMissing f k x a #
(Functor f, Functor g) => Functor (f :*: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> (f :*: g) a -> (f :*: g) b # (<$) :: a -> (f :*: g) b -> (f :*: g) a #
(Functor f, Functor g) => Functor (f :+: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> (f :+: g) a -> (f :+: g) b # (<$) :: a -> (f :+: g) b -> (f :+: g) a #
Functor (K1 i c :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> K1 i c a -> K1 i c b # (<$) :: a -> K1 i c b -> K1 i c a #
Functor (ContT r m) |
Instance details Defined in Control.Monad.Trans.Cont Methods fmap :: (a -> b) -> ContT r m a -> ContT r m b # (<$) :: a -> ContT r m b -> ContT r m a #
Functor ((,,,) a b c) | @since base-4.14.0.0
Instance details Defined in GHC.Internal.Base Methods fmap :: (a0 -> b0) -> (a, b, c, a0) -> (a, b, c, b0) # (<$) :: a0 -> (a, b, c, b0) -> (a, b, c, a0) #
Functor ((->) r) | @since base-2.01
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> (r -> a) -> r -> b # (<$) :: a -> (r -> b) -> r -> a #
(Functor f, Functor g) => Functor (Compose f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Compose Methods fmap :: (a -> b) -> Compose f g a -> Compose f g b # (<$) :: a -> Compose f g b -> Compose f g a #
Functor f => Functor (WhenMatched f k x y) | Since: containers-0.5.9
Instance details Defined in Data.Map.Internal Methods fmap :: (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b # (<$) :: a -> WhenMatched f k x y b -> WhenMatched f k x y a #
(Functor f, Functor g) => Functor (f :.: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> (f :.: g) a -> (f :.: g) b # (<$) :: a -> (f :.: g) b -> (f :.: g) a #
Functor f => Functor (M1 i c f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> M1 i c f a -> M1 i c f b # (<$) :: a -> M1 i c f b -> M1 i c f a #
Functor m => Functor (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.CPS Methods fmap :: (a -> b) -> RWST r w s m a -> RWST r w s m b # (<$) :: a -> RWST r w s m b -> RWST r w s m a #
Functor m => Functor (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.Lazy Methods fmap :: (a -> b) -> RWST r w s m a -> RWST r w s m b # (<$) :: a -> RWST r w s m b -> RWST r w s m a #
Functor m => Functor (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.Strict Methods fmap :: (a -> b) -> RWST r w s m a -> RWST r w s m b # (<$) :: a -> RWST r w s m b -> RWST r w s m a #
Functor ((,,,,) a b c d) | @since base-4.18.0.0
Instance details Defined in GHC.Internal.Base Methods fmap :: (a0 -> b0) -> (a, b, c, d, a0) -> (a, b, c, d, b0) # (<$) :: a0 -> (a, b, c, d, b0) -> (a, b, c, d, a0) #
Functor ((,,,,,) a b c d e) | @since base-4.18.0.0
Instance details Defined in GHC.Internal.Base Methods fmap :: (a0 -> b0) -> (a, b, c, d, e, a0) -> (a, b, c, d, e, b0) # (<$) :: a0 -> (a, b, c, d, e, b0) -> (a, b, c, d, e, a0) #
Functor ((,,,,,,) a b c d e f) | @since base-4.18.0.0
Instance details Defined in GHC.Internal.Base Methods fmap :: (a0 -> b0) -> (a, b, c, d, e, f, a0) -> (a, b, c, d, e, f, b0) # (<$) :: a0 -> (a, b, c, d, e, f, b0) -> (a, b, c, d, e, f, a0) #

class Monad m => MonadFail (m :: Type -> Type) where #

When a value is bound in `do`-notation, the pattern on the left hand side of `<-` might not match. In this case, this class provides a function to recover.

A `Monad` without a `MonadFail` instance may only be used in conjunction with pattern that always match, such as newtypes, tuples, data types with only a single data constructor, and irrefutable patterns (`~pat`).

Instances of `MonadFail` should satisfy the following law: `fail s` should be a left zero for `>>=`,

    fail s >>= f  =  fail s

If your `Monad` is also `MonadPlus`, a popular definition is

    fail _ = mzero

`fail s` should be an action that runs in the monad itself, not an exception (except in instances of `MonadIO`). In particular, `fail` should not be implemented in terms of `error`.

@since base-4.9.0.0

Methods

fail :: String -> m a #

#### Instances

Instances details

MonadFail P | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Text.ParserCombinators.ReadP Methods fail :: String -> P a #
MonadFail ReadP | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Text.ParserCombinators.ReadP Methods fail :: String -> ReadP a #
MonadFail IO | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Control.Monad.Fail Methods fail :: String -> IO a #
MonadFail Array |
Instance details Defined in Data.Primitive.Array Methods fail :: String -> Array a #
MonadFail SmallArray |
Instance details Defined in Data.Primitive.SmallArray Methods fail :: String -> SmallArray a #
MonadFail Vector |
Instance details Defined in Data.Vector Methods fail :: String -> Vector a #
MonadFail Vector |
Instance details Defined in Data.Vector.Strict Methods fail :: String -> Vector a #
MonadFail Maybe | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Control.Monad.Fail Methods fail :: String -> Maybe a #
MonadFail [] | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Control.Monad.Fail Methods fail :: String -> [a] #
Monad m => MonadFail (MaybeT m) |
Instance details Defined in Control.Monad.Trans.Maybe Methods fail :: String -> MaybeT m a #
(Monoid w, MonadFail m) => MonadFail (AccumT w m) |
Instance details Defined in Control.Monad.Trans.Accum Methods fail :: String -> AccumT w m a #
MonadFail m => MonadFail (ExceptT e m) |
Instance details Defined in Control.Monad.Trans.Except Methods fail :: String -> ExceptT e m a #
MonadFail m => MonadFail (IdentityT m) |
Instance details Defined in Control.Monad.Trans.Identity Methods fail :: String -> IdentityT m a #
MonadFail m => MonadFail (ReaderT r m) |
Instance details Defined in Control.Monad.Trans.Reader Methods fail :: String -> ReaderT r m a #
MonadFail m => MonadFail (SelectT r m) |
Instance details Defined in Control.Monad.Trans.Select Methods fail :: String -> SelectT r m a #
MonadFail m => MonadFail (StateT s m) |
Instance details Defined in Control.Monad.Trans.State.Lazy Methods fail :: String -> StateT s m a #
MonadFail m => MonadFail (StateT s m) |
Instance details Defined in Control.Monad.Trans.State.Strict Methods fail :: String -> StateT s m a #
MonadFail m => MonadFail (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.CPS Methods fail :: String -> WriterT w m a #
(Monoid w, MonadFail m) => MonadFail (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods fail :: String -> WriterT w m a #
(Monoid w, MonadFail m) => MonadFail (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods fail :: String -> WriterT w m a #
MonadFail m => MonadFail (Reverse m) |
Instance details Defined in Data.Functor.Reverse Methods fail :: String -> Reverse m a #
MonadFail m => MonadFail (ContT r m) |
Instance details Defined in Control.Monad.Trans.Cont Methods fail :: String -> ContT r m a #
MonadFail m => MonadFail (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.CPS Methods fail :: String -> RWST r w s m a #
(Monoid w, MonadFail m) => MonadFail (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.Lazy Methods fail :: String -> RWST r w s m a #
(Monoid w, MonadFail m) => MonadFail (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.Strict Methods fail :: String -> RWST r w s m a #

guard :: Alternative f => Bool -> f () #

Conditional failure of `Alternative` computations. Defined by

    guard True  = pure ()
    guard False = empty

#### Examples

Expand

Common uses of `guard` include conditionally signalling an error in an error monad and conditionally rejecting the current choice in an `Alternative`-based parser.

As an example of signalling an error in the error monad `Maybe`, consider a safe division function `safeDiv x y` that returns `Nothing` when the denominator `y` is zero and ``Just` (x `div` y)` otherwise. For example:

    >>> safeDiv 4 0
    Nothing

    >>> safeDiv 4 2
    Just 2

A definition of `safeDiv` using guards, but not `guard`:

    safeDiv :: Int -> Int -> Maybe Int
    safeDiv x y | y /= 0    = Just (x `div` y)
                | otherwise = Nothing

A definition of `safeDiv` using `guard` and `Monad` `do`-notation:

    safeDiv :: Int -> Int -> Maybe Int
    safeDiv x y = do
      guard (y /= 0)
      return (x `div` y)

join :: Monad m => m (m a) -> m a #

The `join` function is the conventional monad join operator. It is used to remove one level of monadic structure, projecting its bound argument into the outer level.

'``join` bss`' can be understood as the `do` expression

    do bs <- bss
       bs

#### Examples

Expand

    >>> join [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
    [1,2,3,4,5,6,7,8,9]

    >>> join (Just (Just 3))
    Just 3

A common use of `join` is to run an `IO` computation returned from an `STM` transaction, since `STM` transactions can't perform `IO` directly. Recall that

    atomically :: STM a -> IO a

is used to run `STM` transactions atomically. So, by specializing the types of `atomically` and `join` to

    atomically :: STM (IO b) -> IO (IO b)
    join       :: IO (IO b)  -> IO b

we can compose them as

    join . atomically :: STM (IO b) -> IO b

to run an `STM` transaction and the `IO` action it returns.

class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) where #

Monads that also support choice and failure.

Minimal complete definition

Nothing

Methods

mzero :: m a #

The identity of `mplus`. It should also satisfy the equations

    mzero >>= f  =  mzero
    v >> mzero   =  mzero

The default definition is

    mzero = empty

mplus :: m a -> m a -> m a #

An associative operation. The default definition is

    mplus = (<|>)

#### Instances

Instances details

MonadPlus Seq |
Instance details Defined in Data.Sequence.Internal Methods mzero :: Seq a # mplus :: Seq a -> Seq a -> Seq a #
MonadPlus P | @since base-2.01
Instance details Defined in GHC.Internal.Text.ParserCombinators.ReadP Methods mzero :: P a # mplus :: P a -> P a -> P a #
MonadPlus ReadP | @since base-2.01
Instance details Defined in GHC.Internal.Text.ParserCombinators.ReadP Methods mzero :: ReadP a # mplus :: ReadP a -> ReadP a -> ReadP a #
MonadPlus IO | Takes the first non-throwing `IO` action's result. `mzero` throws an exception. @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods mzero :: IO a # mplus :: IO a -> IO a -> IO a #
MonadPlus Array |
Instance details Defined in Data.Primitive.Array Methods mzero :: Array a # mplus :: Array a -> Array a -> Array a #
MonadPlus SmallArray |
Instance details Defined in Data.Primitive.SmallArray Methods mzero :: SmallArray a # mplus :: SmallArray a -> SmallArray a -> SmallArray a #
MonadPlus Vector |
Instance details Defined in Data.Vector Methods mzero :: Vector a # mplus :: Vector a -> Vector a -> Vector a #
MonadPlus Vector |
Instance details Defined in Data.Vector.Strict Methods mzero :: Vector a # mplus :: Vector a -> Vector a -> Vector a #
MonadPlus Maybe | Picks the leftmost `Just` value, or, alternatively, `Nothing`. @since base-2.01
Instance details Defined in GHC.Internal.Base Methods mzero :: Maybe a # mplus :: Maybe a -> Maybe a -> Maybe a #
MonadPlus [] | Combines lists by concatenation, starting from the empty list. @since base-2.01
Instance details Defined in GHC.Internal.Base Methods mzero :: [a] # mplus :: [a] -> [a] -> [a] #
(ArrowApply a, ArrowPlus a) => MonadPlus (ArrowMonad a) | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Control.Arrow Methods mzero :: ArrowMonad a a0 # mplus :: ArrowMonad a a0 -> ArrowMonad a a0 -> ArrowMonad a a0 #
MonadPlus (U1 :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods mzero :: U1 a # mplus :: U1 a -> U1 a -> U1 a #
Monad m => MonadPlus (MaybeT m) |
Instance details Defined in Control.Monad.Trans.Maybe Methods mzero :: MaybeT m a # mplus :: MaybeT m a -> MaybeT m a -> MaybeT m a #
MonadPlus m => MonadPlus (Kleisli m a) | @since base-4.14.0.0
Instance details Defined in GHC.Internal.Control.Arrow Methods mzero :: Kleisli m a a0 # mplus :: Kleisli m a a0 -> Kleisli m a a0 -> Kleisli m a a0 #
MonadPlus f => MonadPlus (Rec1 f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods mzero :: Rec1 f a # mplus :: Rec1 f a -> Rec1 f a -> Rec1 f a #
(Monoid w, Functor m, MonadPlus m) => MonadPlus (AccumT w m) |
Instance details Defined in Control.Monad.Trans.Accum Methods mzero :: AccumT w m a # mplus :: AccumT w m a -> AccumT w m a -> AccumT w m a #
(Monad m, Monoid e) => MonadPlus (ExceptT e m) |
Instance details Defined in Control.Monad.Trans.Except Methods mzero :: ExceptT e m a # mplus :: ExceptT e m a -> ExceptT e m a -> ExceptT e m a #
MonadPlus m => MonadPlus (IdentityT m) |
Instance details Defined in Control.Monad.Trans.Identity Methods mzero :: IdentityT m a # mplus :: IdentityT m a -> IdentityT m a -> IdentityT m a #
MonadPlus m => MonadPlus (ReaderT r m) |
Instance details Defined in Control.Monad.Trans.Reader Methods mzero :: ReaderT r m a # mplus :: ReaderT r m a -> ReaderT r m a -> ReaderT r m a #
MonadPlus m => MonadPlus (SelectT r m) |
Instance details Defined in Control.Monad.Trans.Select Methods mzero :: SelectT r m a # mplus :: SelectT r m a -> SelectT r m a -> SelectT r m a #
MonadPlus m => MonadPlus (StateT s m) |
Instance details Defined in Control.Monad.Trans.State.Lazy Methods mzero :: StateT s m a # mplus :: StateT s m a -> StateT s m a -> StateT s m a #
MonadPlus m => MonadPlus (StateT s m) |
Instance details Defined in Control.Monad.Trans.State.Strict Methods mzero :: StateT s m a # mplus :: StateT s m a -> StateT s m a -> StateT s m a #
(Functor m, MonadPlus m) => MonadPlus (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.CPS Methods mzero :: WriterT w m a # mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a #
(Monoid w, MonadPlus m) => MonadPlus (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods mzero :: WriterT w m a # mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a #
(Monoid w, MonadPlus m) => MonadPlus (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods mzero :: WriterT w m a # mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a #
MonadPlus m => MonadPlus (Reverse m) | Derived instance.
Instance details Defined in Data.Functor.Reverse Methods mzero :: Reverse m a # mplus :: Reverse m a -> Reverse m a -> Reverse m a #
(MonadPlus f, MonadPlus g) => MonadPlus (Product f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Product Methods mzero :: Product f g a # mplus :: Product f g a -> Product f g a -> Product f g a #
(MonadPlus f, MonadPlus g) => MonadPlus (f :*: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods mzero :: (f :*: g) a # mplus :: (f :*: g) a -> (f :*: g) a -> (f :*: g) a #
MonadPlus f => MonadPlus (M1 i c f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods mzero :: M1 i c f a # mplus :: M1 i c f a -> M1 i c f a -> M1 i c f a #
(Functor m, MonadPlus m) => MonadPlus (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.CPS Methods mzero :: RWST r w s m a # mplus :: RWST r w s m a -> RWST r w s m a -> RWST r w s m a #
(Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.Lazy Methods mzero :: RWST r w s m a # mplus :: RWST r w s m a -> RWST r w s m a -> RWST r w s m a #
(Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) |
Instance details Defined in Control.Monad.Trans.RWS.Strict Methods mzero :: RWST r w s m a # mplus :: RWST r w s m a -> RWST r w s m a -> RWST r w s m a #

(=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1 #

Same as `>>=`, but with the arguments interchanged.

    as >>= f == f =<< as

when :: Applicative f => Bool -> f () -> f () #

Conditional execution of `Applicative` expressions. For example,

#### Examples

Expand

    when debug (putStrLn "Debugging")

will output the string `Debugging` if the Boolean value `debug` is `True`, and otherwise do nothing.

    >>> putStr "pi:" >> when False (print 3.14159)
    pi:

liftM :: Monad m => (a1 -> r) -> m a1 -> m r #

Promote a function to a monad. This is equivalent to `fmap` but specialised to Monads.

liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r #

Promote a function to a monad, scanning the monadic arguments from left to right.

#### Examples

Expand

    >>> liftM2 (+) [0,1] [0,2]
    [0,2,1,3]

    >>> liftM2 (+) (Just 1) Nothing
    Nothing

    >>> liftM2 (+) (+ 3) (* 2) 5
    18

liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r #

Promote a function to a monad, scanning the monadic arguments from left to right (cf. `liftM2`).

liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r #

Promote a function to a monad, scanning the monadic arguments from left to right (cf. `liftM2`).

liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r #

Promote a function to a monad, scanning the monadic arguments from left to right (cf. `liftM2`).

ap :: Monad m => m (a -> b) -> m a -> m b #

In many situations, the `liftM` operations can be replaced by uses of `ap`, which promotes function application.

    return f `ap` x1 `ap` ... `ap` xn

is equivalent to

    liftM<n> f x1 x2 ... xn

#### Examples

Expand

    >>> pure (\x y z -> x + y * z) `ap` Just 1 `ap` Just 5 `ap` Just 10
    Just 51

void :: Functor f => f a -> f () #

``void` value` discards or ignores the result of evaluation, such as the return value of an `IO` action.

#### Examples

Expand

Replace the contents of a ``Maybe` `Int`` with unit:

    >>> void Nothing
    Nothing

    >>> void (Just 3)
    Just ()

Replace the contents of an ``Either` `Int` `Int`` with unit, resulting in an ``Either` `Int` `()``:

    >>> void (Left 8675309)
    Left 8675309

    >>> void (Right 8675309)
    Right ()

Replace every element of a list with unit:

    >>> void [1,2,3]
    [(),(),()]

Replace the second element of a pair with unit:

    >>> void (1,2)
    (1,())

Discard the result of an `IO` action:

    >>> mapM print [1,2]
    1
    2
    [(),()]

    >>> void $ mapM print [1,2]
    1
    2

mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m () #

Map each element of a structure to a monadic action, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results see `mapM`.

`mapM_` is just like `traverse_`, but specialised to monadic actions.

forM_ :: (Foldable t, Monad m) => t a -> (a -> m b) -> m () #

`forM_` is `mapM_` with its arguments flipped. For a version that doesn't ignore the results see `forM`.

`forM_` is just like `for_`, but specialised to monadic actions.

sequence_ :: (Foldable t, Monad m) => t (m a) -> m () #

Evaluate each monadic action in the structure from left to right, and ignore the results. For a version that doesn't ignore the results see `sequence`.

`sequence_` is just like `sequenceA_`, but specialised to monadic actions.

msum :: (Foldable t, MonadPlus m) => t (m a) -> m a #

The sum of a collection of actions using `(<|>)`, generalizing `concat`.

`msum` is just like `asum`, but specialised to `MonadPlus`.

#### Examples

Expand

Basic usage, using the `MonadPlus` instance for `Maybe`:

    >>> msum [Just "Hello", Nothing, Just "World"]
    Just "Hello"

forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b) #

`forM` is `mapM` with its arguments flipped. For a version that ignores the results see `forM_`.

filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a] #

This generalizes the list-based `filter` function.

    runIdentity (filterM (Identity . p) xs) == filter p xs

#### Examples

Expand

    >>> filterM (\x -> do
          putStrLn ("Keep: " ++ show x ++ "?")
          answer <- getLine
          pure (answer == "y"))
        [1, 2, 3]
    Keep: 1?
    y
    Keep: 2?
    n
    Keep: 3?
    y
    [1,3]

    >>> filterM (\x -> do
          putStr (show x)
          x' <- readLn
          pure (x == x'))
        [1, 2, 3]
    12
    22
    33
    [2,3]

(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c infixr 1 #

Left-to-right composition of `Kleisli` arrows.

'`(bs `>=>` cs) a`' can be understood as the `do` expression

    do b <- bs a
       cs b

or in terms of ``(>>=)`` as

    bs a >>= cs

(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c infixr 1 #

Right-to-left composition of Kleisli arrows. `(`>=>`)`, with the arguments flipped.

Note how this operator resembles function composition `(`.`)`:

    (.)   ::            (b ->   c) -> (a ->   b) -> a ->   c
    (<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c

forever :: Applicative f => f a -> f b #

Repeat an action indefinitely.

#### Examples

Expand

A common use of `forever` is to process input from network sockets, `Handle`s, and channels (e.g. `MVar` and `Chan`).

For example, here is how we might implement an echo server, using `forever` both to listen for client connections on a network socket and to echo client input on client connection handles:

    echoServer :: Socket -> IO ()
    echoServer socket = forever $ do
      client <- accept socket
      forkFinally (echo client) (\_ -> hClose client)
      where
        echo :: Handle -> IO ()
        echo client = forever $
          hGetLine client >>= hPutStrLn client

Note that "forever" isn't necessarily non-terminating. If the action is in a ``MonadPlus`` and short-circuits after some number of iterations. then ``forever`` actually returns `mzero`, effectively short-circuiting its caller.

mapAndUnzipM :: Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c]) #

The `mapAndUnzipM` function maps its first argument over a list, returning the result as a pair of lists. This function is mainly used with complicated data structures or a state monad.

zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c] #

The `zipWithM` function generalizes `zipWith` to arbitrary applicative functors.

zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m () #

`zipWithM_` is the extension of `zipWithM` which ignores the final result.

foldM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b #

The `foldM` function is analogous to `foldl`, except that its result is encapsulated in a monad. Note that `foldM` works from left-to-right over the list arguments. This could be an issue where `(`>>`)` and the `folded function' are not commutative.

    foldM f a1 [x1, x2, ..., xm]

    ==

    do
      a2 <- f a1 x1
      a3 <- f a2 x2
      ...
      f am xm

If right-to-left evaluation is required, the input list should be reversed.

Note: `foldM` is the same as `foldlM`

foldM_ :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m () #

Like `foldM`, but discards the result.

replicateM :: Applicative m => Int -> m a -> m [a] #

``replicateM` n act` performs the action `act` `n` times, and then returns the list of results.

    replicateM n (pure x) == replicate n x

#### Examples

Expand

    >>> replicateM 3 getLine
    hi
    heya
    hiya
    ["hi","heya","hiya"]

    >>> import Control.Monad.State
    >>> runState (replicateM 3 $ state $ \s -> (s, s + 1)) 1
    ([1,2,3],4)

replicateM_ :: Applicative m => Int -> m a -> m () #

Like `replicateM`, but discards the result.

#### Examples

Expand

    >>> replicateM_ 3 (putStr "a")
    aaa

unless :: Applicative f => Bool -> f () -> f () #

The reverse of `when`.

#### Examples

Expand

    >>> do x <- getLine
           unless (x == "hi") (putStrLn "hi!")
    comingupwithexamplesisdifficult
    hi!

    >>> unless (pi > exp 1) Nothing
    Just ()

(<$!>) :: Monad m => (a -> b) -> m a -> m b infixl 4 #

Strict version of `<$>`.

@since base-4.8.0.0

mfilter :: MonadPlus m => (a -> Bool) -> m a -> m a #

Direct `MonadPlus` equivalent of `filter`.

#### Examples

Expand

The `filter` function is just `mfilter` specialized to the list monad:

    filter = ( mfilter :: (a -> Bool) -> [a] -> [a] )

An example using `mfilter` with the `Maybe` monad:

    >>> mfilter odd (Just 1)
    Just 1
    >>> mfilter odd (Just 2)
    Nothing

## Folds and traversals

class Foldable (t :: Type -> Type) where #

The Foldable class represents data structures that can be reduced to a summary value one element at a time. Strict left-associative folds are a good fit for space-efficient reduction, while lazy right-associative folds are a good fit for corecursive iteration, or for folds that short-circuit after processing an initial subsequence of the structure's elements.

Instances can be derived automatically by enabling the `DeriveFoldable` extension. For example, a derived instance for a binary tree might be:

    {-# LANGUAGE DeriveFoldable #-}
    data Tree a = Empty
                | Leaf a
                | Node (Tree a) a (Tree a)
        deriving Foldable

A more detailed description can be found in the Overview section of Data.Foldable.

For the class laws see the Laws section of Data.Foldable.

Minimal complete definition

foldMap | foldr

Methods

foldMap :: Monoid m => (a -> m) -> t a -> m #

Map each element of the structure into a monoid, and combine the results with `(`<>`)`. This fold is right-associative and lazy in the accumulator. For strict left-associative folds consider `foldMap'` instead.

#### Examples

Expand

Basic usage:

    >>> foldMap Sum [1, 3, 5]
    Sum {getSum = 9}

    >>> foldMap Product [1, 3, 5]
    Product {getProduct = 15}

    >>> foldMap (replicate 3) [1, 2, 3]
    [1,1,1,2,2,2,3,3,3]

When a Monoid's `(`<>`)` is lazy in its second argument, `foldMap` can return a result even from an unbounded structure. For example, lazy accumulation enables Data.ByteString.Builder to efficiently serialise large data structures and produce the output incrementally:

    >>> import qualified Data.ByteString.Lazy as L
    >>> import qualified Data.ByteString.Builder as B
    >>> let bld :: Int -> B.Builder; bld i = B.intDec i <> B.word8 0x20
    >>> let lbs = B.toLazyByteString $ foldMap bld [0..]
    >>> L.take 64 lbs
    "0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24"

foldr :: (a -> b -> b) -> b -> t a -> b #

Right-associative fold of a structure, lazy in the accumulator.

In the case of lists, `foldr`, when applied to a binary operator, a starting value (typically the right-identity of the operator), and a list, reduces the list using the binary operator, from right to left:

    foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)

Note that since the head of the resulting expression is produced by an application of the operator to the first element of the list, given an operator lazy in its right argument, `foldr` can produce a terminating expression from an unbounded list.

For a general `Foldable` structure this should be semantically identical to,

    foldr f z = foldr f z . toList

#### Examples

Expand

Basic usage:

    >>> foldr (||) False [False, True, False]
    True

    >>> foldr (||) False []
    False

    >>> foldr (\c acc -> acc ++ [c]) "foo" ['a', 'b', 'c', 'd']
    "foodcba"

##### Infinite structures

⚠️ Applying `foldr` to infinite structures usually doesn't terminate.

It may still terminate under one of the following conditions:

- the folding function is short-circuiting
- the folding function is lazy on its second argument

###### Short-circuiting

`(`||`)` short-circuits on `True` values, so the following terminates because there is a `True` value finitely far from the left side:

    >>> foldr (||) False (True : repeat False)
    True

But the following doesn't terminate:

    >>> foldr (||) False (repeat False ++ [True])
    * Hangs forever *

###### Laziness in the second argument

Applying `foldr` to infinite structures terminates when the operator is lazy in its second argument (the initial accumulator is never used in this case, and so could be left `undefined`, but `[]` is more clear):

    >>> take 5 $ foldr (\i acc -> i : fmap (+3) acc) [] (repeat 1)
    [1,4,7,10,13]

foldr' :: (a -> b -> b) -> b -> t a -> b #

`foldr'` is a variant of `foldr` that performs strict reduction from right to left, i.e. starting with the right-most element. The input structure must be finite, otherwise `foldr'` runs out of space (diverges).

If you want a strict right fold in constant space, you need a structure that supports faster than O(n) access to the right-most element, such as `Seq` from the `containers` package.

This method does not run in constant space for structures such as lists that don't support efficient right-to-left iteration and so require O(n) space to perform right-to-left reduction. Use of this method with such a structure is a hint that the chosen structure may be a poor fit for the task at hand. If the order in which the elements are combined is not important, use `foldl'` instead.

@since base-4.6.0.0

foldl :: (b -> a -> b) -> b -> t a -> b #

Left-associative fold of a structure, lazy in the accumulator. This is rarely what you want, but can work well for structures with efficient right-to-left sequencing and an operator that is lazy in its left argument.

In the case of lists, `foldl`, when applied to a binary operator, a starting value (typically the left-identity of the operator), and a list, reduces the list using the binary operator, from left to right:

    foldl f z [x1, x2, ..., xn] == (...((z `f` x1) `f` x2) `f`...) `f` xn

Note that to produce the outermost application of the operator the entire input list must be traversed. Like all left-associative folds, `foldl` will diverge if given an infinite list.

If you want an efficient strict left-fold, you probably want to use `foldl'` instead of `foldl`. The reason for this is that the latter does not force the inner results (e.g. `z `f` x1` in the above example) before applying them to the operator (e.g. to `(`f` x2)`). This results in a thunk chain O(n) elements long, which then must be evaluated from the outside-in.

For a general `Foldable` structure this should be semantically identical to:

    foldl f z = foldl f z . toList

#### Examples

Expand

The first example is a strict fold, which in practice is best performed with `foldl'`.

    >>> foldl (+) 42 [1,2,3,4]
    52

Though the result below is lazy, the input is reversed before prepending it to the initial accumulator, so corecursion begins only after traversing the entire input string.

    >>> foldl (\acc c -> c : acc) "abcd" "efgh"
    "hgfeabcd"

A left fold of a structure that is infinite on the right cannot terminate, even when for any finite input the fold just returns the initial accumulator:

    >>> foldl (\a _ -> a) 0 $ repeat 1
    * Hangs forever *

WARNING: When it comes to lists, you always want to use either `foldl'` or `foldr` instead.

foldl' :: (b -> a -> b) -> b -> t a -> b #

Left-associative fold of a structure but with strict application of the operator.

This ensures that each step of the fold is forced to Weak Head Normal Form before being applied, avoiding the collection of thunks that would otherwise occur. This is often what you want to strictly reduce a finite structure to a single strict result (e.g. `sum`).

For a general `Foldable` structure this should be semantically identical to,

    foldl' f z = foldl' f z . toList

@since base-4.6.0.0

foldr1 :: (a -> a -> a) -> t a -> a #

A variant of `foldr` that has no base case, and thus may only be applied to non-empty structures.

This function is non-total and will raise a runtime exception if the structure happens to be empty.

#### Examples

Expand

Basic usage:

    >>> foldr1 (+) [1..4]
    10

    >>> foldr1 (+) []
    Exception: Prelude.foldr1: empty list

    >>> foldr1 (+) Nothing
    *** Exception: foldr1: empty structure

    >>> foldr1 (-) [1..4]
    -2

    >>> foldr1 (&&) [True, False, True, True]
    False

    >>> foldr1 (||) [False, False, True, True]
    True

    >>> foldr1 (+) [1..]
    * Hangs forever *

foldl1 :: (a -> a -> a) -> t a -> a #

A variant of `foldl` that has no base case, and thus may only be applied to non-empty structures.

This function is non-total and will raise a runtime exception if the structure happens to be empty.

    foldl1 f = foldl1 f . toList

#### Examples

Expand

Basic usage:

    >>> foldl1 (+) [1..4]
    10

    >>> foldl1 (+) []
    *** Exception: Prelude.foldl1: empty list

    >>> foldl1 (+) Nothing
    *** Exception: foldl1: empty structure

    >>> foldl1 (-) [1..4]
    -8

    >>> foldl1 (&&) [True, False, True, True]
    False

    >>> foldl1 (||) [False, False, True, True]
    True

    >>> foldl1 (+) [1..]
    * Hangs forever *

#### Instances

Instances details

Foldable Complex | Since: base-4.9.0.0
Instance details Defined in Data.Complex Methods fold :: Monoid m => Complex m -> m # foldMap :: Monoid m => (a -> m) -> Complex a -> m # foldMap' :: Monoid m => (a -> m) -> Complex a -> m # foldr :: (a -> b -> b) -> b -> Complex a -> b # foldr' :: (a -> b -> b) -> b -> Complex a -> b # foldl :: (b -> a -> b) -> b -> Complex a -> b # foldl' :: (b -> a -> b) -> b -> Complex a -> b # foldr1 :: (a -> a -> a) -> Complex a -> a # foldl1 :: (a -> a -> a) -> Complex a -> a # toList :: Complex a -> [a] # null :: Complex a -> Bool # length :: Complex a -> Int # elem :: Eq a => a -> Complex a -> Bool # maximum :: Ord a => Complex a -> a # minimum :: Ord a => Complex a -> a # sum :: Num a => Complex a -> a # product :: Num a => Complex a -> a #
Foldable First | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fold :: Monoid m => First m -> m # foldMap :: Monoid m => (a -> m) -> First a -> m # foldMap' :: Monoid m => (a -> m) -> First a -> m # foldr :: (a -> b -> b) -> b -> First a -> b # foldr' :: (a -> b -> b) -> b -> First a -> b # foldl :: (b -> a -> b) -> b -> First a -> b # foldl' :: (b -> a -> b) -> b -> First a -> b # foldr1 :: (a -> a -> a) -> First a -> a # foldl1 :: (a -> a -> a) -> First a -> a # toList :: First a -> [a] # null :: First a -> Bool # length :: First a -> Int # elem :: Eq a => a -> First a -> Bool # maximum :: Ord a => First a -> a # minimum :: Ord a => First a -> a # sum :: Num a => First a -> a # product :: Num a => First a -> a #
Foldable Last | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fold :: Monoid m => Last m -> m # foldMap :: Monoid m => (a -> m) -> Last a -> m # foldMap' :: Monoid m => (a -> m) -> Last a -> m # foldr :: (a -> b -> b) -> b -> Last a -> b # foldr' :: (a -> b -> b) -> b -> Last a -> b # foldl :: (b -> a -> b) -> b -> Last a -> b # foldl' :: (b -> a -> b) -> b -> Last a -> b # foldr1 :: (a -> a -> a) -> Last a -> a # foldl1 :: (a -> a -> a) -> Last a -> a # toList :: Last a -> [a] # null :: Last a -> Bool # length :: Last a -> Int # elem :: Eq a => a -> Last a -> Bool # maximum :: Ord a => Last a -> a # minimum :: Ord a => Last a -> a # sum :: Num a => Last a -> a # product :: Num a => Last a -> a #
Foldable Max | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fold :: Monoid m => Max m -> m # foldMap :: Monoid m => (a -> m) -> Max a -> m # foldMap' :: Monoid m => (a -> m) -> Max a -> m # foldr :: (a -> b -> b) -> b -> Max a -> b # foldr' :: (a -> b -> b) -> b -> Max a -> b # foldl :: (b -> a -> b) -> b -> Max a -> b # foldl' :: (b -> a -> b) -> b -> Max a -> b # foldr1 :: (a -> a -> a) -> Max a -> a # foldl1 :: (a -> a -> a) -> Max a -> a # toList :: Max a -> [a] # null :: Max a -> Bool # length :: Max a -> Int # elem :: Eq a => a -> Max a -> Bool # maximum :: Ord a => Max a -> a # minimum :: Ord a => Max a -> a # sum :: Num a => Max a -> a # product :: Num a => Max a -> a #
Foldable Min | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fold :: Monoid m => Min m -> m # foldMap :: Monoid m => (a -> m) -> Min a -> m # foldMap' :: Monoid m => (a -> m) -> Min a -> m # foldr :: (a -> b -> b) -> b -> Min a -> b # foldr' :: (a -> b -> b) -> b -> Min a -> b # foldl :: (b -> a -> b) -> b -> Min a -> b # foldl' :: (b -> a -> b) -> b -> Min a -> b # foldr1 :: (a -> a -> a) -> Min a -> a # foldl1 :: (a -> a -> a) -> Min a -> a # toList :: Min a -> [a] # null :: Min a -> Bool # length :: Min a -> Int # elem :: Eq a => a -> Min a -> Bool # maximum :: Ord a => Min a -> a # minimum :: Ord a => Min a -> a # sum :: Num a => Min a -> a # product :: Num a => Min a -> a #
Foldable SCC | Since: containers-0.5.9
Instance details Defined in Data.Graph Methods fold :: Monoid m => SCC m -> m # foldMap :: Monoid m => (a -> m) -> SCC a -> m # foldMap' :: Monoid m => (a -> m) -> SCC a -> m # foldr :: (a -> b -> b) -> b -> SCC a -> b # foldr' :: (a -> b -> b) -> b -> SCC a -> b # foldl :: (b -> a -> b) -> b -> SCC a -> b # foldl' :: (b -> a -> b) -> b -> SCC a -> b # foldr1 :: (a -> a -> a) -> SCC a -> a # foldl1 :: (a -> a -> a) -> SCC a -> a # toList :: SCC a -> [a] # null :: SCC a -> Bool # length :: SCC a -> Int # elem :: Eq a => a -> SCC a -> Bool # maximum :: Ord a => SCC a -> a # minimum :: Ord a => SCC a -> a # sum :: Num a => SCC a -> a # product :: Num a => SCC a -> a #
Foldable IntMap | Folds in order of increasing key.
Instance details Defined in Data.IntMap.Internal Methods fold :: Monoid m => IntMap m -> m # foldMap :: Monoid m => (a -> m) -> IntMap a -> m # foldMap' :: Monoid m => (a -> m) -> IntMap a -> m # foldr :: (a -> b -> b) -> b -> IntMap a -> b # foldr' :: (a -> b -> b) -> b -> IntMap a -> b # foldl :: (b -> a -> b) -> b -> IntMap a -> b # foldl' :: (b -> a -> b) -> b -> IntMap a -> b # foldr1 :: (a -> a -> a) -> IntMap a -> a # foldl1 :: (a -> a -> a) -> IntMap a -> a # toList :: IntMap a -> [a] # null :: IntMap a -> Bool # length :: IntMap a -> Int # elem :: Eq a => a -> IntMap a -> Bool # maximum :: Ord a => IntMap a -> a # minimum :: Ord a => IntMap a -> a # sum :: Num a => IntMap a -> a # product :: Num a => IntMap a -> a #
Foldable Digit |
Instance details Defined in Data.Sequence.Internal Methods fold :: Monoid m => Digit m -> m # foldMap :: Monoid m => (a -> m) -> Digit a -> m # foldMap' :: Monoid m => (a -> m) -> Digit a -> m # foldr :: (a -> b -> b) -> b -> Digit a -> b # foldr' :: (a -> b -> b) -> b -> Digit a -> b # foldl :: (b -> a -> b) -> b -> Digit a -> b # foldl' :: (b -> a -> b) -> b -> Digit a -> b # foldr1 :: (a -> a -> a) -> Digit a -> a # foldl1 :: (a -> a -> a) -> Digit a -> a # toList :: Digit a -> [a] # null :: Digit a -> Bool # length :: Digit a -> Int # elem :: Eq a => a -> Digit a -> Bool # maximum :: Ord a => Digit a -> a # minimum :: Ord a => Digit a -> a # sum :: Num a => Digit a -> a # product :: Num a => Digit a -> a #
Foldable Elem |
Instance details Defined in Data.Sequence.Internal Methods fold :: Monoid m => Elem m -> m # foldMap :: Monoid m => (a -> m) -> Elem a -> m # foldMap' :: Monoid m => (a -> m) -> Elem a -> m # foldr :: (a -> b -> b) -> b -> Elem a -> b # foldr' :: (a -> b -> b) -> b -> Elem a -> b # foldl :: (b -> a -> b) -> b -> Elem a -> b # foldl' :: (b -> a -> b) -> b -> Elem a -> b # foldr1 :: (a -> a -> a) -> Elem a -> a # foldl1 :: (a -> a -> a) -> Elem a -> a # toList :: Elem a -> [a] # null :: Elem a -> Bool # length :: Elem a -> Int # elem :: Eq a => a -> Elem a -> Bool # maximum :: Ord a => Elem a -> a # minimum :: Ord a => Elem a -> a # sum :: Num a => Elem a -> a # product :: Num a => Elem a -> a #
Foldable FingerTree |
Instance details Defined in Data.Sequence.Internal Methods fold :: Monoid m => FingerTree m -> m # foldMap :: Monoid m => (a -> m) -> FingerTree a -> m # foldMap' :: Monoid m => (a -> m) -> FingerTree a -> m # foldr :: (a -> b -> b) -> b -> FingerTree a -> b # foldr' :: (a -> b -> b) -> b -> FingerTree a -> b # foldl :: (b -> a -> b) -> b -> FingerTree a -> b # foldl' :: (b -> a -> b) -> b -> FingerTree a -> b # foldr1 :: (a -> a -> a) -> FingerTree a -> a # foldl1 :: (a -> a -> a) -> FingerTree a -> a # toList :: FingerTree a -> [a] # null :: FingerTree a -> Bool # length :: FingerTree a -> Int # elem :: Eq a => a -> FingerTree a -> Bool # maximum :: Ord a => FingerTree a -> a # minimum :: Ord a => FingerTree a -> a # sum :: Num a => FingerTree a -> a # product :: Num a => FingerTree a -> a #
Foldable Node |
Instance details Defined in Data.Sequence.Internal Methods fold :: Monoid m => Node m -> m # foldMap :: Monoid m => (a -> m) -> Node a -> m # foldMap' :: Monoid m => (a -> m) -> Node a -> m # foldr :: (a -> b -> b) -> b -> Node a -> b # foldr' :: (a -> b -> b) -> b -> Node a -> b # foldl :: (b -> a -> b) -> b -> Node a -> b # foldl' :: (b -> a -> b) -> b -> Node a -> b # foldr1 :: (a -> a -> a) -> Node a -> a # foldl1 :: (a -> a -> a) -> Node a -> a # toList :: Node a -> [a] # null :: Node a -> Bool # length :: Node a -> Int # elem :: Eq a => a -> Node a -> Bool # maximum :: Ord a => Node a -> a # minimum :: Ord a => Node a -> a # sum :: Num a => Node a -> a # product :: Num a => Node a -> a #
Foldable Seq |
Instance details Defined in Data.Sequence.Internal Methods fold :: Monoid m => Seq m -> m # foldMap :: Monoid m => (a -> m) -> Seq a -> m # foldMap' :: Monoid m => (a -> m) -> Seq a -> m # foldr :: (a -> b -> b) -> b -> Seq a -> b # foldr' :: (a -> b -> b) -> b -> Seq a -> b # foldl :: (b -> a -> b) -> b -> Seq a -> b # foldl' :: (b -> a -> b) -> b -> Seq a -> b # foldr1 :: (a -> a -> a) -> Seq a -> a # foldl1 :: (a -> a -> a) -> Seq a -> a # toList :: Seq a -> [a] # null :: Seq a -> Bool # length :: Seq a -> Int # elem :: Eq a => a -> Seq a -> Bool # maximum :: Ord a => Seq a -> a # minimum :: Ord a => Seq a -> a # sum :: Num a => Seq a -> a # product :: Num a => Seq a -> a #
Foldable ViewL |
Instance details Defined in Data.Sequence.Internal Methods fold :: Monoid m => ViewL m -> m # foldMap :: Monoid m => (a -> m) -> ViewL a -> m # foldMap' :: Monoid m => (a -> m) -> ViewL a -> m # foldr :: (a -> b -> b) -> b -> ViewL a -> b # foldr' :: (a -> b -> b) -> b -> ViewL a -> b # foldl :: (b -> a -> b) -> b -> ViewL a -> b # foldl' :: (b -> a -> b) -> b -> ViewL a -> b # foldr1 :: (a -> a -> a) -> ViewL a -> a # foldl1 :: (a -> a -> a) -> ViewL a -> a # toList :: ViewL a -> [a] # null :: ViewL a -> Bool # length :: ViewL a -> Int # elem :: Eq a => a -> ViewL a -> Bool # maximum :: Ord a => ViewL a -> a # minimum :: Ord a => ViewL a -> a # sum :: Num a => ViewL a -> a # product :: Num a => ViewL a -> a #
Foldable ViewR |
Instance details Defined in Data.Sequence.Internal Methods fold :: Monoid m => ViewR m -> m # foldMap :: Monoid m => (a -> m) -> ViewR a -> m # foldMap' :: Monoid m => (a -> m) -> ViewR a -> m # foldr :: (a -> b -> b) -> b -> ViewR a -> b # foldr' :: (a -> b -> b) -> b -> ViewR a -> b # foldl :: (b -> a -> b) -> b -> ViewR a -> b # foldl' :: (b -> a -> b) -> b -> ViewR a -> b # foldr1 :: (a -> a -> a) -> ViewR a -> a # foldl1 :: (a -> a -> a) -> ViewR a -> a # toList :: ViewR a -> [a] # null :: ViewR a -> Bool # length :: ViewR a -> Int # elem :: Eq a => a -> ViewR a -> Bool # maximum :: Ord a => ViewR a -> a # minimum :: Ord a => ViewR a -> a # sum :: Num a => ViewR a -> a # product :: Num a => ViewR a -> a #
Foldable Set | Folds in order of increasing key.
Instance details Defined in Data.Set.Internal Methods fold :: Monoid m => Set m -> m # foldMap :: Monoid m => (a -> m) -> Set a -> m # foldMap' :: Monoid m => (a -> m) -> Set a -> m # foldr :: (a -> b -> b) -> b -> Set a -> b # foldr' :: (a -> b -> b) -> b -> Set a -> b # foldl :: (b -> a -> b) -> b -> Set a -> b # foldl' :: (b -> a -> b) -> b -> Set a -> b # foldr1 :: (a -> a -> a) -> Set a -> a # foldl1 :: (a -> a -> a) -> Set a -> a # toList :: Set a -> [a] # null :: Set a -> Bool # length :: Set a -> Int # elem :: Eq a => a -> Set a -> Bool # maximum :: Ord a => Set a -> a # minimum :: Ord a => Set a -> a # sum :: Num a => Set a -> a # product :: Num a => Set a -> a #
Foldable Tree | Folds in preorder
Instance details Defined in Data.Tree Methods fold :: Monoid m => Tree m -> m # foldMap :: Monoid m => (a -> m) -> Tree a -> m # foldMap' :: Monoid m => (a -> m) -> Tree a -> m # foldr :: (a -> b -> b) -> b -> Tree a -> b # foldr' :: (a -> b -> b) -> b -> Tree a -> b # foldl :: (b -> a -> b) -> b -> Tree a -> b # foldl' :: (b -> a -> b) -> b -> Tree a -> b # foldr1 :: (a -> a -> a) -> Tree a -> a # foldl1 :: (a -> a -> a) -> Tree a -> a # toList :: Tree a -> [a] # null :: Tree a -> Bool # length :: Tree a -> Int # elem :: Eq a => a -> Tree a -> Bool # maximum :: Ord a => Tree a -> a # minimum :: Ord a => Tree a -> a # sum :: Num a => Tree a -> a # product :: Num a => Tree a -> a #
Foldable NonEmpty | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => NonEmpty m -> m # foldMap :: Monoid m => (a -> m) -> NonEmpty a -> m # foldMap' :: Monoid m => (a -> m) -> NonEmpty a -> m # foldr :: (a -> b -> b) -> b -> NonEmpty a -> b # foldr' :: (a -> b -> b) -> b -> NonEmpty a -> b # foldl :: (b -> a -> b) -> b -> NonEmpty a -> b # foldl' :: (b -> a -> b) -> b -> NonEmpty a -> b # foldr1 :: (a -> a -> a) -> NonEmpty a -> a # foldl1 :: (a -> a -> a) -> NonEmpty a -> a # toList :: NonEmpty a -> [a] # null :: NonEmpty a -> Bool # length :: NonEmpty a -> Int # elem :: Eq a => a -> NonEmpty a -> Bool # maximum :: Ord a => NonEmpty a -> a # minimum :: Ord a => NonEmpty a -> a # sum :: Num a => NonEmpty a -> a # product :: Num a => NonEmpty a -> a #
Foldable First | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => First m -> m # foldMap :: Monoid m => (a -> m) -> First a -> m # foldMap' :: Monoid m => (a -> m) -> First a -> m # foldr :: (a -> b -> b) -> b -> First a -> b # foldr' :: (a -> b -> b) -> b -> First a -> b # foldl :: (b -> a -> b) -> b -> First a -> b # foldl' :: (b -> a -> b) -> b -> First a -> b # foldr1 :: (a -> a -> a) -> First a -> a # foldl1 :: (a -> a -> a) -> First a -> a # toList :: First a -> [a] # null :: First a -> Bool # length :: First a -> Int # elem :: Eq a => a -> First a -> Bool # maximum :: Ord a => First a -> a # minimum :: Ord a => First a -> a # sum :: Num a => First a -> a # product :: Num a => First a -> a #
Foldable Last | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Last m -> m # foldMap :: Monoid m => (a -> m) -> Last a -> m # foldMap' :: Monoid m => (a -> m) -> Last a -> m # foldr :: (a -> b -> b) -> b -> Last a -> b # foldr' :: (a -> b -> b) -> b -> Last a -> b # foldl :: (b -> a -> b) -> b -> Last a -> b # foldl' :: (b -> a -> b) -> b -> Last a -> b # foldr1 :: (a -> a -> a) -> Last a -> a # foldl1 :: (a -> a -> a) -> Last a -> a # toList :: Last a -> [a] # null :: Last a -> Bool # length :: Last a -> Int # elem :: Eq a => a -> Last a -> Bool # maximum :: Ord a => Last a -> a # minimum :: Ord a => Last a -> a # sum :: Num a => Last a -> a # product :: Num a => Last a -> a #
Foldable Down | @since base-4.12.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Down m -> m # foldMap :: Monoid m => (a -> m) -> Down a -> m # foldMap' :: Monoid m => (a -> m) -> Down a -> m # foldr :: (a -> b -> b) -> b -> Down a -> b # foldr' :: (a -> b -> b) -> b -> Down a -> b # foldl :: (b -> a -> b) -> b -> Down a -> b # foldl' :: (b -> a -> b) -> b -> Down a -> b # foldr1 :: (a -> a -> a) -> Down a -> a # foldl1 :: (a -> a -> a) -> Down a -> a # toList :: Down a -> [a] # null :: Down a -> Bool # length :: Down a -> Int # elem :: Eq a => a -> Down a -> Bool # maximum :: Ord a => Down a -> a # minimum :: Ord a => Down a -> a # sum :: Num a => Down a -> a # product :: Num a => Down a -> a #
Foldable Dual | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Dual m -> m # foldMap :: Monoid m => (a -> m) -> Dual a -> m # foldMap' :: Monoid m => (a -> m) -> Dual a -> m # foldr :: (a -> b -> b) -> b -> Dual a -> b # foldr' :: (a -> b -> b) -> b -> Dual a -> b # foldl :: (b -> a -> b) -> b -> Dual a -> b # foldl' :: (b -> a -> b) -> b -> Dual a -> b # foldr1 :: (a -> a -> a) -> Dual a -> a # foldl1 :: (a -> a -> a) -> Dual a -> a # toList :: Dual a -> [a] # null :: Dual a -> Bool # length :: Dual a -> Int # elem :: Eq a => a -> Dual a -> Bool # maximum :: Ord a => Dual a -> a # minimum :: Ord a => Dual a -> a # sum :: Num a => Dual a -> a # product :: Num a => Dual a -> a #
Foldable Product | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Product m -> m # foldMap :: Monoid m => (a -> m) -> Product a -> m # foldMap' :: Monoid m => (a -> m) -> Product a -> m # foldr :: (a -> b -> b) -> b -> Product a -> b # foldr' :: (a -> b -> b) -> b -> Product a -> b # foldl :: (b -> a -> b) -> b -> Product a -> b # foldl' :: (b -> a -> b) -> b -> Product a -> b # foldr1 :: (a -> a -> a) -> Product a -> a # foldl1 :: (a -> a -> a) -> Product a -> a # toList :: Product a -> [a] # null :: Product a -> Bool # length :: Product a -> Int # elem :: Eq a => a -> Product a -> Bool # maximum :: Ord a => Product a -> a # minimum :: Ord a => Product a -> a # sum :: Num a => Product a -> a # product :: Num a => Product a -> a #
Foldable Sum | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Sum m -> m # foldMap :: Monoid m => (a -> m) -> Sum a -> m # foldMap' :: Monoid m => (a -> m) -> Sum a -> m # foldr :: (a -> b -> b) -> b -> Sum a -> b # foldr' :: (a -> b -> b) -> b -> Sum a -> b # foldl :: (b -> a -> b) -> b -> Sum a -> b # foldl' :: (b -> a -> b) -> b -> Sum a -> b # foldr1 :: (a -> a -> a) -> Sum a -> a # foldl1 :: (a -> a -> a) -> Sum a -> a # toList :: Sum a -> [a] # null :: Sum a -> Bool # length :: Sum a -> Int # elem :: Eq a => a -> Sum a -> Bool # maximum :: Ord a => Sum a -> a # minimum :: Ord a => Sum a -> a # sum :: Num a => Sum a -> a # product :: Num a => Sum a -> a #
Foldable Par1 | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Par1 m -> m # foldMap :: Monoid m => (a -> m) -> Par1 a -> m # foldMap' :: Monoid m => (a -> m) -> Par1 a -> m # foldr :: (a -> b -> b) -> b -> Par1 a -> b # foldr' :: (a -> b -> b) -> b -> Par1 a -> b # foldl :: (b -> a -> b) -> b -> Par1 a -> b # foldl' :: (b -> a -> b) -> b -> Par1 a -> b # foldr1 :: (a -> a -> a) -> Par1 a -> a # foldl1 :: (a -> a -> a) -> Par1 a -> a # toList :: Par1 a -> [a] # null :: Par1 a -> Bool # length :: Par1 a -> Int # elem :: Eq a => a -> Par1 a -> Bool # maximum :: Ord a => Par1 a -> a # minimum :: Ord a => Par1 a -> a # sum :: Num a => Par1 a -> a # product :: Num a => Par1 a -> a #
Foldable Hashed |
Instance details Defined in Data.Hashable.Class Methods fold :: Monoid m => Hashed m -> m # foldMap :: Monoid m => (a -> m) -> Hashed a -> m # foldMap' :: Monoid m => (a -> m) -> Hashed a -> m # foldr :: (a -> b -> b) -> b -> Hashed a -> b # foldr' :: (a -> b -> b) -> b -> Hashed a -> b # foldl :: (b -> a -> b) -> b -> Hashed a -> b # foldl' :: (b -> a -> b) -> b -> Hashed a -> b # foldr1 :: (a -> a -> a) -> Hashed a -> a # foldl1 :: (a -> a -> a) -> Hashed a -> a # toList :: Hashed a -> [a] # null :: Hashed a -> Bool # length :: Hashed a -> Int # elem :: Eq a => a -> Hashed a -> Bool # maximum :: Ord a => Hashed a -> a # minimum :: Ord a => Hashed a -> a # sum :: Num a => Hashed a -> a # product :: Num a => Hashed a -> a #
Foldable Array |
Instance details Defined in Data.Primitive.Array Methods fold :: Monoid m => Array m -> m # foldMap :: Monoid m => (a -> m) -> Array a -> m # foldMap' :: Monoid m => (a -> m) -> Array a -> m # foldr :: (a -> b -> b) -> b -> Array a -> b # foldr' :: (a -> b -> b) -> b -> Array a -> b # foldl :: (b -> a -> b) -> b -> Array a -> b # foldl' :: (b -> a -> b) -> b -> Array a -> b # foldr1 :: (a -> a -> a) -> Array a -> a # foldl1 :: (a -> a -> a) -> Array a -> a # toList :: Array a -> [a] # null :: Array a -> Bool # length :: Array a -> Int # elem :: Eq a => a -> Array a -> Bool # maximum :: Ord a => Array a -> a # minimum :: Ord a => Array a -> a # sum :: Num a => Array a -> a # product :: Num a => Array a -> a #
Foldable SmallArray |
Instance details Defined in Data.Primitive.SmallArray Methods fold :: Monoid m => SmallArray m -> m # foldMap :: Monoid m => (a -> m) -> SmallArray a -> m # foldMap' :: Monoid m => (a -> m) -> SmallArray a -> m # foldr :: (a -> b -> b) -> b -> SmallArray a -> b # foldr' :: (a -> b -> b) -> b -> SmallArray a -> b # foldl :: (b -> a -> b) -> b -> SmallArray a -> b # foldl' :: (b -> a -> b) -> b -> SmallArray a -> b # foldr1 :: (a -> a -> a) -> SmallArray a -> a # foldl1 :: (a -> a -> a) -> SmallArray a -> a # toList :: SmallArray a -> [a] # null :: SmallArray a -> Bool # length :: SmallArray a -> Int # elem :: Eq a => a -> SmallArray a -> Bool # maximum :: Ord a => SmallArray a -> a # minimum :: Ord a => SmallArray a -> a # sum :: Num a => SmallArray a -> a # product :: Num a => SmallArray a -> a #
Foldable HashSet |
Instance details Defined in Data.HashSet.Internal Methods fold :: Monoid m => HashSet m -> m # foldMap :: Monoid m => (a -> m) -> HashSet a -> m # foldMap' :: Monoid m => (a -> m) -> HashSet a -> m # foldr :: (a -> b -> b) -> b -> HashSet a -> b # foldr' :: (a -> b -> b) -> b -> HashSet a -> b # foldl :: (b -> a -> b) -> b -> HashSet a -> b # foldl' :: (b -> a -> b) -> b -> HashSet a -> b # foldr1 :: (a -> a -> a) -> HashSet a -> a # foldl1 :: (a -> a -> a) -> HashSet a -> a # toList :: HashSet a -> [a] # null :: HashSet a -> Bool # length :: HashSet a -> Int # elem :: Eq a => a -> HashSet a -> Bool # maximum :: Ord a => HashSet a -> a # minimum :: Ord a => HashSet a -> a # sum :: Num a => HashSet a -> a # product :: Num a => HashSet a -> a #
Foldable Vector |
Instance details Defined in Data.Vector Methods fold :: Monoid m => Vector m -> m # foldMap :: Monoid m => (a -> m) -> Vector a -> m # foldMap' :: Monoid m => (a -> m) -> Vector a -> m # foldr :: (a -> b -> b) -> b -> Vector a -> b # foldr' :: (a -> b -> b) -> b -> Vector a -> b # foldl :: (b -> a -> b) -> b -> Vector a -> b # foldl' :: (b -> a -> b) -> b -> Vector a -> b # foldr1 :: (a -> a -> a) -> Vector a -> a # foldl1 :: (a -> a -> a) -> Vector a -> a # toList :: Vector a -> [a] # null :: Vector a -> Bool # length :: Vector a -> Int # elem :: Eq a => a -> Vector a -> Bool # maximum :: Ord a => Vector a -> a # minimum :: Ord a => Vector a -> a # sum :: Num a => Vector a -> a # product :: Num a => Vector a -> a #
Foldable Vector |
Instance details Defined in Data.Vector.Strict Methods fold :: Monoid m => Vector m -> m # foldMap :: Monoid m => (a -> m) -> Vector a -> m # foldMap' :: Monoid m => (a -> m) -> Vector a -> m # foldr :: (a -> b -> b) -> b -> Vector a -> b # foldr' :: (a -> b -> b) -> b -> Vector a -> b # foldl :: (b -> a -> b) -> b -> Vector a -> b # foldl' :: (b -> a -> b) -> b -> Vector a -> b # foldr1 :: (a -> a -> a) -> Vector a -> a # foldl1 :: (a -> a -> a) -> Vector a -> a # toList :: Vector a -> [a] # null :: Vector a -> Bool # length :: Vector a -> Int # elem :: Eq a => a -> Vector a -> Bool # maximum :: Ord a => Vector a -> a # minimum :: Ord a => Vector a -> a # sum :: Num a => Vector a -> a # product :: Num a => Vector a -> a #
Foldable Maybe | @since base-2.01
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Maybe m -> m # foldMap :: Monoid m => (a -> m) -> Maybe a -> m # foldMap' :: Monoid m => (a -> m) -> Maybe a -> m # foldr :: (a -> b -> b) -> b -> Maybe a -> b # foldr' :: (a -> b -> b) -> b -> Maybe a -> b # foldl :: (b -> a -> b) -> b -> Maybe a -> b # foldl' :: (b -> a -> b) -> b -> Maybe a -> b # foldr1 :: (a -> a -> a) -> Maybe a -> a # foldl1 :: (a -> a -> a) -> Maybe a -> a # toList :: Maybe a -> [a] # null :: Maybe a -> Bool # length :: Maybe a -> Int # elem :: Eq a => a -> Maybe a -> Bool # maximum :: Ord a => Maybe a -> a # minimum :: Ord a => Maybe a -> a # sum :: Num a => Maybe a -> a # product :: Num a => Maybe a -> a #
Foldable Solo | @since base-4.15
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Solo m -> m # foldMap :: Monoid m => (a -> m) -> Solo a -> m # foldMap' :: Monoid m => (a -> m) -> Solo a -> m # foldr :: (a -> b -> b) -> b -> Solo a -> b # foldr' :: (a -> b -> b) -> b -> Solo a -> b # foldl :: (b -> a -> b) -> b -> Solo a -> b # foldl' :: (b -> a -> b) -> b -> Solo a -> b # foldr1 :: (a -> a -> a) -> Solo a -> a # foldl1 :: (a -> a -> a) -> Solo a -> a # toList :: Solo a -> [a] # null :: Solo a -> Bool # length :: Solo a -> Int # elem :: Eq a => a -> Solo a -> Bool # maximum :: Ord a => Solo a -> a # minimum :: Ord a => Solo a -> a # sum :: Num a => Solo a -> a # product :: Num a => Solo a -> a #
Foldable [] | @since base-2.01
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => [m] -> m # foldMap :: Monoid m => (a -> m) -> [a] -> m # foldMap' :: Monoid m => (a -> m) -> [a] -> m # foldr :: (a -> b -> b) -> b -> [a] -> b # foldr' :: (a -> b -> b) -> b -> [a] -> b # foldl :: (b -> a -> b) -> b -> [a] -> b # foldl' :: (b -> a -> b) -> b -> [a] -> b # foldr1 :: (a -> a -> a) -> [a] -> a # foldl1 :: (a -> a -> a) -> [a] -> a # toList :: [a] -> [a] # null :: [a] -> Bool # length :: [a] -> Int # elem :: Eq a => a -> [a] -> Bool # maximum :: Ord a => [a] -> a # minimum :: Ord a => [a] -> a # sum :: Num a => [a] -> a # product :: Num a => [a] -> a #
Foldable (Arg a) | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods fold :: Monoid m => Arg a m -> m # foldMap :: Monoid m => (a0 -> m) -> Arg a a0 -> m # foldMap' :: Monoid m => (a0 -> m) -> Arg a a0 -> m # foldr :: (a0 -> b -> b) -> b -> Arg a a0 -> b # foldr' :: (a0 -> b -> b) -> b -> Arg a a0 -> b # foldl :: (b -> a0 -> b) -> b -> Arg a a0 -> b # foldl' :: (b -> a0 -> b) -> b -> Arg a a0 -> b # foldr1 :: (a0 -> a0 -> a0) -> Arg a a0 -> a0 # foldl1 :: (a0 -> a0 -> a0) -> Arg a a0 -> a0 # toList :: Arg a a0 -> [a0] # null :: Arg a a0 -> Bool # length :: Arg a a0 -> Int # elem :: Eq a0 => a0 -> Arg a a0 -> Bool # maximum :: Ord a0 => Arg a a0 -> a0 # minimum :: Ord a0 => Arg a a0 -> a0 # sum :: Num a0 => Arg a a0 -> a0 # product :: Num a0 => Arg a a0 -> a0 #
Foldable (Map k) | Folds in order of increasing key.
Instance details Defined in Data.Map.Internal Methods fold :: Monoid m => Map k m -> m # foldMap :: Monoid m => (a -> m) -> Map k a -> m # foldMap' :: Monoid m => (a -> m) -> Map k a -> m # foldr :: (a -> b -> b) -> b -> Map k a -> b # foldr' :: (a -> b -> b) -> b -> Map k a -> b # foldl :: (b -> a -> b) -> b -> Map k a -> b # foldl' :: (b -> a -> b) -> b -> Map k a -> b # foldr1 :: (a -> a -> a) -> Map k a -> a # foldl1 :: (a -> a -> a) -> Map k a -> a # toList :: Map k a -> [a] # null :: Map k a -> Bool # length :: Map k a -> Int # elem :: Eq a => a -> Map k a -> Bool # maximum :: Ord a => Map k a -> a # minimum :: Ord a => Map k a -> a # sum :: Num a => Map k a -> a # product :: Num a => Map k a -> a #
Foldable (Array i) | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Array i m -> m # foldMap :: Monoid m => (a -> m) -> Array i a -> m # foldMap' :: Monoid m => (a -> m) -> Array i a -> m # foldr :: (a -> b -> b) -> b -> Array i a -> b # foldr' :: (a -> b -> b) -> b -> Array i a -> b # foldl :: (b -> a -> b) -> b -> Array i a -> b # foldl' :: (b -> a -> b) -> b -> Array i a -> b # foldr1 :: (a -> a -> a) -> Array i a -> a # foldl1 :: (a -> a -> a) -> Array i a -> a # toList :: Array i a -> [a] # null :: Array i a -> Bool # length :: Array i a -> Int # elem :: Eq a => a -> Array i a -> Bool # maximum :: Ord a => Array i a -> a # minimum :: Ord a => Array i a -> a # sum :: Num a => Array i a -> a # product :: Num a => Array i a -> a #
Foldable (Either a) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Either a m -> m # foldMap :: Monoid m => (a0 -> m) -> Either a a0 -> m # foldMap' :: Monoid m => (a0 -> m) -> Either a a0 -> m # foldr :: (a0 -> b -> b) -> b -> Either a a0 -> b # foldr' :: (a0 -> b -> b) -> b -> Either a a0 -> b # foldl :: (b -> a0 -> b) -> b -> Either a a0 -> b # foldl' :: (b -> a0 -> b) -> b -> Either a a0 -> b # foldr1 :: (a0 -> a0 -> a0) -> Either a a0 -> a0 # foldl1 :: (a0 -> a0 -> a0) -> Either a a0 -> a0 # toList :: Either a a0 -> [a0] # null :: Either a a0 -> Bool # length :: Either a a0 -> Int # elem :: Eq a0 => a0 -> Either a a0 -> Bool # maximum :: Ord a0 => Either a a0 -> a0 # minimum :: Ord a0 => Either a a0 -> a0 # sum :: Num a0 => Either a a0 -> a0 # product :: Num a0 => Either a a0 -> a0 #
Foldable (Proxy :: Type -> Type) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Proxy m -> m # foldMap :: Monoid m => (a -> m) -> Proxy a -> m # foldMap' :: Monoid m => (a -> m) -> Proxy a -> m # foldr :: (a -> b -> b) -> b -> Proxy a -> b # foldr' :: (a -> b -> b) -> b -> Proxy a -> b # foldl :: (b -> a -> b) -> b -> Proxy a -> b # foldl' :: (b -> a -> b) -> b -> Proxy a -> b # foldr1 :: (a -> a -> a) -> Proxy a -> a # foldl1 :: (a -> a -> a) -> Proxy a -> a # toList :: Proxy a -> [a] # null :: Proxy a -> Bool # length :: Proxy a -> Int # elem :: Eq a => a -> Proxy a -> Bool # maximum :: Ord a => Proxy a -> a # minimum :: Ord a => Proxy a -> a # sum :: Num a => Proxy a -> a # product :: Num a => Proxy a -> a #
Foldable (U1 :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => U1 m -> m # foldMap :: Monoid m => (a -> m) -> U1 a -> m # foldMap' :: Monoid m => (a -> m) -> U1 a -> m # foldr :: (a -> b -> b) -> b -> U1 a -> b # foldr' :: (a -> b -> b) -> b -> U1 a -> b # foldl :: (b -> a -> b) -> b -> U1 a -> b # foldl' :: (b -> a -> b) -> b -> U1 a -> b # foldr1 :: (a -> a -> a) -> U1 a -> a # foldl1 :: (a -> a -> a) -> U1 a -> a # toList :: U1 a -> [a] # null :: U1 a -> Bool # length :: U1 a -> Int # elem :: Eq a => a -> U1 a -> Bool # maximum :: Ord a => U1 a -> a # minimum :: Ord a => U1 a -> a # sum :: Num a => U1 a -> a # product :: Num a => U1 a -> a #
Foldable (UAddr :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => UAddr m -> m # foldMap :: Monoid m => (a -> m) -> UAddr a -> m # foldMap' :: Monoid m => (a -> m) -> UAddr a -> m # foldr :: (a -> b -> b) -> b -> UAddr a -> b # foldr' :: (a -> b -> b) -> b -> UAddr a -> b # foldl :: (b -> a -> b) -> b -> UAddr a -> b # foldl' :: (b -> a -> b) -> b -> UAddr a -> b # foldr1 :: (a -> a -> a) -> UAddr a -> a # foldl1 :: (a -> a -> a) -> UAddr a -> a # toList :: UAddr a -> [a] # null :: UAddr a -> Bool # length :: UAddr a -> Int # elem :: Eq a => a -> UAddr a -> Bool # maximum :: Ord a => UAddr a -> a # minimum :: Ord a => UAddr a -> a # sum :: Num a => UAddr a -> a # product :: Num a => UAddr a -> a #
Foldable (UChar :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => UChar m -> m # foldMap :: Monoid m => (a -> m) -> UChar a -> m # foldMap' :: Monoid m => (a -> m) -> UChar a -> m # foldr :: (a -> b -> b) -> b -> UChar a -> b # foldr' :: (a -> b -> b) -> b -> UChar a -> b # foldl :: (b -> a -> b) -> b -> UChar a -> b # foldl' :: (b -> a -> b) -> b -> UChar a -> b # foldr1 :: (a -> a -> a) -> UChar a -> a # foldl1 :: (a -> a -> a) -> UChar a -> a # toList :: UChar a -> [a] # null :: UChar a -> Bool # length :: UChar a -> Int # elem :: Eq a => a -> UChar a -> Bool # maximum :: Ord a => UChar a -> a # minimum :: Ord a => UChar a -> a # sum :: Num a => UChar a -> a # product :: Num a => UChar a -> a #
Foldable (UDouble :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => UDouble m -> m # foldMap :: Monoid m => (a -> m) -> UDouble a -> m # foldMap' :: Monoid m => (a -> m) -> UDouble a -> m # foldr :: (a -> b -> b) -> b -> UDouble a -> b # foldr' :: (a -> b -> b) -> b -> UDouble a -> b # foldl :: (b -> a -> b) -> b -> UDouble a -> b # foldl' :: (b -> a -> b) -> b -> UDouble a -> b # foldr1 :: (a -> a -> a) -> UDouble a -> a # foldl1 :: (a -> a -> a) -> UDouble a -> a # toList :: UDouble a -> [a] # null :: UDouble a -> Bool # length :: UDouble a -> Int # elem :: Eq a => a -> UDouble a -> Bool # maximum :: Ord a => UDouble a -> a # minimum :: Ord a => UDouble a -> a # sum :: Num a => UDouble a -> a # product :: Num a => UDouble a -> a #
Foldable (UFloat :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => UFloat m -> m # foldMap :: Monoid m => (a -> m) -> UFloat a -> m # foldMap' :: Monoid m => (a -> m) -> UFloat a -> m # foldr :: (a -> b -> b) -> b -> UFloat a -> b # foldr' :: (a -> b -> b) -> b -> UFloat a -> b # foldl :: (b -> a -> b) -> b -> UFloat a -> b # foldl' :: (b -> a -> b) -> b -> UFloat a -> b # foldr1 :: (a -> a -> a) -> UFloat a -> a # foldl1 :: (a -> a -> a) -> UFloat a -> a # toList :: UFloat a -> [a] # null :: UFloat a -> Bool # length :: UFloat a -> Int # elem :: Eq a => a -> UFloat a -> Bool # maximum :: Ord a => UFloat a -> a # minimum :: Ord a => UFloat a -> a # sum :: Num a => UFloat a -> a # product :: Num a => UFloat a -> a #
Foldable (UInt :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => UInt m -> m # foldMap :: Monoid m => (a -> m) -> UInt a -> m # foldMap' :: Monoid m => (a -> m) -> UInt a -> m # foldr :: (a -> b -> b) -> b -> UInt a -> b # foldr' :: (a -> b -> b) -> b -> UInt a -> b # foldl :: (b -> a -> b) -> b -> UInt a -> b # foldl' :: (b -> a -> b) -> b -> UInt a -> b # foldr1 :: (a -> a -> a) -> UInt a -> a # foldl1 :: (a -> a -> a) -> UInt a -> a # toList :: UInt a -> [a] # null :: UInt a -> Bool # length :: UInt a -> Int # elem :: Eq a => a -> UInt a -> Bool # maximum :: Ord a => UInt a -> a # minimum :: Ord a => UInt a -> a # sum :: Num a => UInt a -> a # product :: Num a => UInt a -> a #
Foldable (UWord :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => UWord m -> m # foldMap :: Monoid m => (a -> m) -> UWord a -> m # foldMap' :: Monoid m => (a -> m) -> UWord a -> m # foldr :: (a -> b -> b) -> b -> UWord a -> b # foldr' :: (a -> b -> b) -> b -> UWord a -> b # foldl :: (b -> a -> b) -> b -> UWord a -> b # foldl' :: (b -> a -> b) -> b -> UWord a -> b # foldr1 :: (a -> a -> a) -> UWord a -> a # foldl1 :: (a -> a -> a) -> UWord a -> a # toList :: UWord a -> [a] # null :: UWord a -> Bool # length :: UWord a -> Int # elem :: Eq a => a -> UWord a -> Bool # maximum :: Ord a => UWord a -> a # minimum :: Ord a => UWord a -> a # sum :: Num a => UWord a -> a # product :: Num a => UWord a -> a #
Foldable (V1 :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => V1 m -> m # foldMap :: Monoid m => (a -> m) -> V1 a -> m # foldMap' :: Monoid m => (a -> m) -> V1 a -> m # foldr :: (a -> b -> b) -> b -> V1 a -> b # foldr' :: (a -> b -> b) -> b -> V1 a -> b # foldl :: (b -> a -> b) -> b -> V1 a -> b # foldl' :: (b -> a -> b) -> b -> V1 a -> b # foldr1 :: (a -> a -> a) -> V1 a -> a # foldl1 :: (a -> a -> a) -> V1 a -> a # toList :: V1 a -> [a] # null :: V1 a -> Bool # length :: V1 a -> Int # elem :: Eq a => a -> V1 a -> Bool # maximum :: Ord a => V1 a -> a # minimum :: Ord a => V1 a -> a # sum :: Num a => V1 a -> a # product :: Num a => V1 a -> a #
Foldable f => Foldable (Lift f) |
Instance details Defined in Control.Applicative.Lift Methods fold :: Monoid m => Lift f m -> m # foldMap :: Monoid m => (a -> m) -> Lift f a -> m # foldMap' :: Monoid m => (a -> m) -> Lift f a -> m # foldr :: (a -> b -> b) -> b -> Lift f a -> b # foldr' :: (a -> b -> b) -> b -> Lift f a -> b # foldl :: (b -> a -> b) -> b -> Lift f a -> b # foldl' :: (b -> a -> b) -> b -> Lift f a -> b # foldr1 :: (a -> a -> a) -> Lift f a -> a # foldl1 :: (a -> a -> a) -> Lift f a -> a # toList :: Lift f a -> [a] # null :: Lift f a -> Bool # length :: Lift f a -> Int # elem :: Eq a => a -> Lift f a -> Bool # maximum :: Ord a => Lift f a -> a # minimum :: Ord a => Lift f a -> a # sum :: Num a => Lift f a -> a # product :: Num a => Lift f a -> a #
Foldable f => Foldable (MaybeT f) |
Instance details Defined in Control.Monad.Trans.Maybe Methods fold :: Monoid m => MaybeT f m -> m # foldMap :: Monoid m => (a -> m) -> MaybeT f a -> m # foldMap' :: Monoid m => (a -> m) -> MaybeT f a -> m # foldr :: (a -> b -> b) -> b -> MaybeT f a -> b # foldr' :: (a -> b -> b) -> b -> MaybeT f a -> b # foldl :: (b -> a -> b) -> b -> MaybeT f a -> b # foldl' :: (b -> a -> b) -> b -> MaybeT f a -> b # foldr1 :: (a -> a -> a) -> MaybeT f a -> a # foldl1 :: (a -> a -> a) -> MaybeT f a -> a # toList :: MaybeT f a -> [a] # null :: MaybeT f a -> Bool # length :: MaybeT f a -> Int # elem :: Eq a => a -> MaybeT f a -> Bool # maximum :: Ord a => MaybeT f a -> a # minimum :: Ord a => MaybeT f a -> a # sum :: Num a => MaybeT f a -> a # product :: Num a => MaybeT f a -> a #
Foldable (HashMap k) |
Instance details Defined in Data.HashMap.Internal Methods fold :: Monoid m => HashMap k m -> m # foldMap :: Monoid m => (a -> m) -> HashMap k a -> m # foldMap' :: Monoid m => (a -> m) -> HashMap k a -> m # foldr :: (a -> b -> b) -> b -> HashMap k a -> b # foldr' :: (a -> b -> b) -> b -> HashMap k a -> b # foldl :: (b -> a -> b) -> b -> HashMap k a -> b # foldl' :: (b -> a -> b) -> b -> HashMap k a -> b # foldr1 :: (a -> a -> a) -> HashMap k a -> a # foldl1 :: (a -> a -> a) -> HashMap k a -> a # toList :: HashMap k a -> [a] # null :: HashMap k a -> Bool # length :: HashMap k a -> Int # elem :: Eq a => a -> HashMap k a -> Bool # maximum :: Ord a => HashMap k a -> a # minimum :: Ord a => HashMap k a -> a # sum :: Num a => HashMap k a -> a # product :: Num a => HashMap k a -> a #
Foldable ((,) a) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => (a, m) -> m # foldMap :: Monoid m => (a0 -> m) -> (a, a0) -> m # foldMap' :: Monoid m => (a0 -> m) -> (a, a0) -> m # foldr :: (a0 -> b -> b) -> b -> (a, a0) -> b # foldr' :: (a0 -> b -> b) -> b -> (a, a0) -> b # foldl :: (b -> a0 -> b) -> b -> (a, a0) -> b # foldl' :: (b -> a0 -> b) -> b -> (a, a0) -> b # foldr1 :: (a0 -> a0 -> a0) -> (a, a0) -> a0 # foldl1 :: (a0 -> a0 -> a0) -> (a, a0) -> a0 # toList :: (a, a0) -> [a0] # null :: (a, a0) -> Bool # length :: (a, a0) -> Int # elem :: Eq a0 => a0 -> (a, a0) -> Bool # maximum :: Ord a0 => (a, a0) -> a0 # minimum :: Ord a0 => (a, a0) -> a0 # sum :: Num a0 => (a, a0) -> a0 # product :: Num a0 => (a, a0) -> a0 #
Foldable f => Foldable (Ap f) | @since base-4.12.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Ap f m -> m # foldMap :: Monoid m => (a -> m) -> Ap f a -> m # foldMap' :: Monoid m => (a -> m) -> Ap f a -> m # foldr :: (a -> b -> b) -> b -> Ap f a -> b # foldr' :: (a -> b -> b) -> b -> Ap f a -> b # foldl :: (b -> a -> b) -> b -> Ap f a -> b # foldl' :: (b -> a -> b) -> b -> Ap f a -> b # foldr1 :: (a -> a -> a) -> Ap f a -> a # foldl1 :: (a -> a -> a) -> Ap f a -> a # toList :: Ap f a -> [a] # null :: Ap f a -> Bool # length :: Ap f a -> Int # elem :: Eq a => a -> Ap f a -> Bool # maximum :: Ord a => Ap f a -> a # minimum :: Ord a => Ap f a -> a # sum :: Num a => Ap f a -> a # product :: Num a => Ap f a -> a #
Foldable f => Foldable (Alt f) | @since base-4.12.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Alt f m -> m # foldMap :: Monoid m => (a -> m) -> Alt f a -> m # foldMap' :: Monoid m => (a -> m) -> Alt f a -> m # foldr :: (a -> b -> b) -> b -> Alt f a -> b # foldr' :: (a -> b -> b) -> b -> Alt f a -> b # foldl :: (b -> a -> b) -> b -> Alt f a -> b # foldl' :: (b -> a -> b) -> b -> Alt f a -> b # foldr1 :: (a -> a -> a) -> Alt f a -> a # foldl1 :: (a -> a -> a) -> Alt f a -> a # toList :: Alt f a -> [a] # null :: Alt f a -> Bool # length :: Alt f a -> Int # elem :: Eq a => a -> Alt f a -> Bool # maximum :: Ord a => Alt f a -> a # minimum :: Ord a => Alt f a -> a # sum :: Num a => Alt f a -> a # product :: Num a => Alt f a -> a #
Foldable f => Foldable (Rec1 f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => Rec1 f m -> m # foldMap :: Monoid m => (a -> m) -> Rec1 f a -> m # foldMap' :: Monoid m => (a -> m) -> Rec1 f a -> m # foldr :: (a -> b -> b) -> b -> Rec1 f a -> b # foldr' :: (a -> b -> b) -> b -> Rec1 f a -> b # foldl :: (b -> a -> b) -> b -> Rec1 f a -> b # foldl' :: (b -> a -> b) -> b -> Rec1 f a -> b # foldr1 :: (a -> a -> a) -> Rec1 f a -> a # foldl1 :: (a -> a -> a) -> Rec1 f a -> a # toList :: Rec1 f a -> [a] # null :: Rec1 f a -> Bool # length :: Rec1 f a -> Int # elem :: Eq a => a -> Rec1 f a -> Bool # maximum :: Ord a => Rec1 f a -> a # minimum :: Ord a => Rec1 f a -> a # sum :: Num a => Rec1 f a -> a # product :: Num a => Rec1 f a -> a #
Foldable f => Foldable (Backwards f) | Derived instance.
Instance details Defined in Control.Applicative.Backwards Methods fold :: Monoid m => Backwards f m -> m # foldMap :: Monoid m => (a -> m) -> Backwards f a -> m # foldMap' :: Monoid m => (a -> m) -> Backwards f a -> m # foldr :: (a -> b -> b) -> b -> Backwards f a -> b # foldr' :: (a -> b -> b) -> b -> Backwards f a -> b # foldl :: (b -> a -> b) -> b -> Backwards f a -> b # foldl' :: (b -> a -> b) -> b -> Backwards f a -> b # foldr1 :: (a -> a -> a) -> Backwards f a -> a # foldl1 :: (a -> a -> a) -> Backwards f a -> a # toList :: Backwards f a -> [a] # null :: Backwards f a -> Bool # length :: Backwards f a -> Int # elem :: Eq a => a -> Backwards f a -> Bool # maximum :: Ord a => Backwards f a -> a # minimum :: Ord a => Backwards f a -> a # sum :: Num a => Backwards f a -> a # product :: Num a => Backwards f a -> a #
Foldable f => Foldable (ExceptT e f) |
Instance details Defined in Control.Monad.Trans.Except Methods fold :: Monoid m => ExceptT e f m -> m # foldMap :: Monoid m => (a -> m) -> ExceptT e f a -> m # foldMap' :: Monoid m => (a -> m) -> ExceptT e f a -> m # foldr :: (a -> b -> b) -> b -> ExceptT e f a -> b # foldr' :: (a -> b -> b) -> b -> ExceptT e f a -> b # foldl :: (b -> a -> b) -> b -> ExceptT e f a -> b # foldl' :: (b -> a -> b) -> b -> ExceptT e f a -> b # foldr1 :: (a -> a -> a) -> ExceptT e f a -> a # foldl1 :: (a -> a -> a) -> ExceptT e f a -> a # toList :: ExceptT e f a -> [a] # null :: ExceptT e f a -> Bool # length :: ExceptT e f a -> Int # elem :: Eq a => a -> ExceptT e f a -> Bool # maximum :: Ord a => ExceptT e f a -> a # minimum :: Ord a => ExceptT e f a -> a # sum :: Num a => ExceptT e f a -> a # product :: Num a => ExceptT e f a -> a #
Foldable f => Foldable (IdentityT f) |
Instance details Defined in Control.Monad.Trans.Identity Methods fold :: Monoid m => IdentityT f m -> m # foldMap :: Monoid m => (a -> m) -> IdentityT f a -> m # foldMap' :: Monoid m => (a -> m) -> IdentityT f a -> m # foldr :: (a -> b -> b) -> b -> IdentityT f a -> b # foldr' :: (a -> b -> b) -> b -> IdentityT f a -> b # foldl :: (b -> a -> b) -> b -> IdentityT f a -> b # foldl' :: (b -> a -> b) -> b -> IdentityT f a -> b # foldr1 :: (a -> a -> a) -> IdentityT f a -> a # foldl1 :: (a -> a -> a) -> IdentityT f a -> a # toList :: IdentityT f a -> [a] # null :: IdentityT f a -> Bool # length :: IdentityT f a -> Int # elem :: Eq a => a -> IdentityT f a -> Bool # maximum :: Ord a => IdentityT f a -> a # minimum :: Ord a => IdentityT f a -> a # sum :: Num a => IdentityT f a -> a # product :: Num a => IdentityT f a -> a #
Foldable f => Foldable (WriterT w f) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods fold :: Monoid m => WriterT w f m -> m # foldMap :: Monoid m => (a -> m) -> WriterT w f a -> m # foldMap' :: Monoid m => (a -> m) -> WriterT w f a -> m # foldr :: (a -> b -> b) -> b -> WriterT w f a -> b # foldr' :: (a -> b -> b) -> b -> WriterT w f a -> b # foldl :: (b -> a -> b) -> b -> WriterT w f a -> b # foldl' :: (b -> a -> b) -> b -> WriterT w f a -> b # foldr1 :: (a -> a -> a) -> WriterT w f a -> a # foldl1 :: (a -> a -> a) -> WriterT w f a -> a # toList :: WriterT w f a -> [a] # null :: WriterT w f a -> Bool # length :: WriterT w f a -> Int # elem :: Eq a => a -> WriterT w f a -> Bool # maximum :: Ord a => WriterT w f a -> a # minimum :: Ord a => WriterT w f a -> a # sum :: Num a => WriterT w f a -> a # product :: Num a => WriterT w f a -> a #
Foldable f => Foldable (WriterT w f) |
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods fold :: Monoid m => WriterT w f m -> m # foldMap :: Monoid m => (a -> m) -> WriterT w f a -> m # foldMap' :: Monoid m => (a -> m) -> WriterT w f a -> m # foldr :: (a -> b -> b) -> b -> WriterT w f a -> b # foldr' :: (a -> b -> b) -> b -> WriterT w f a -> b # foldl :: (b -> a -> b) -> b -> WriterT w f a -> b # foldl' :: (b -> a -> b) -> b -> WriterT w f a -> b # foldr1 :: (a -> a -> a) -> WriterT w f a -> a # foldl1 :: (a -> a -> a) -> WriterT w f a -> a # toList :: WriterT w f a -> [a] # null :: WriterT w f a -> Bool # length :: WriterT w f a -> Int # elem :: Eq a => a -> WriterT w f a -> Bool # maximum :: Ord a => WriterT w f a -> a # minimum :: Ord a => WriterT w f a -> a # sum :: Num a => WriterT w f a -> a # product :: Num a => WriterT w f a -> a #
Foldable (Constant a :: Type -> Type) |
Instance details Defined in Data.Functor.Constant Methods fold :: Monoid m => Constant a m -> m # foldMap :: Monoid m => (a0 -> m) -> Constant a a0 -> m # foldMap' :: Monoid m => (a0 -> m) -> Constant a a0 -> m # foldr :: (a0 -> b -> b) -> b -> Constant a a0 -> b # foldr' :: (a0 -> b -> b) -> b -> Constant a a0 -> b # foldl :: (b -> a0 -> b) -> b -> Constant a a0 -> b # foldl' :: (b -> a0 -> b) -> b -> Constant a a0 -> b # foldr1 :: (a0 -> a0 -> a0) -> Constant a a0 -> a0 # foldl1 :: (a0 -> a0 -> a0) -> Constant a a0 -> a0 # toList :: Constant a a0 -> [a0] # null :: Constant a a0 -> Bool # length :: Constant a a0 -> Int # elem :: Eq a0 => a0 -> Constant a a0 -> Bool # maximum :: Ord a0 => Constant a a0 -> a0 # minimum :: Ord a0 => Constant a a0 -> a0 # sum :: Num a0 => Constant a a0 -> a0 # product :: Num a0 => Constant a a0 -> a0 #
Foldable f => Foldable (Reverse f) | Fold from right to left.
Instance details Defined in Data.Functor.Reverse Methods fold :: Monoid m => Reverse f m -> m # foldMap :: Monoid m => (a -> m) -> Reverse f a -> m # foldMap' :: Monoid m => (a -> m) -> Reverse f a -> m # foldr :: (a -> b -> b) -> b -> Reverse f a -> b # foldr' :: (a -> b -> b) -> b -> Reverse f a -> b # foldl :: (b -> a -> b) -> b -> Reverse f a -> b # foldl' :: (b -> a -> b) -> b -> Reverse f a -> b # foldr1 :: (a -> a -> a) -> Reverse f a -> a # foldl1 :: (a -> a -> a) -> Reverse f a -> a # toList :: Reverse f a -> [a] # null :: Reverse f a -> Bool # length :: Reverse f a -> Int # elem :: Eq a => a -> Reverse f a -> Bool # maximum :: Ord a => Reverse f a -> a # minimum :: Ord a => Reverse f a -> a # sum :: Num a => Reverse f a -> a # product :: Num a => Reverse f a -> a #
(Foldable f, Foldable g) => Foldable (Product f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Product Methods fold :: Monoid m => Product f g m -> m # foldMap :: Monoid m => (a -> m) -> Product f g a -> m # foldMap' :: Monoid m => (a -> m) -> Product f g a -> m # foldr :: (a -> b -> b) -> b -> Product f g a -> b # foldr' :: (a -> b -> b) -> b -> Product f g a -> b # foldl :: (b -> a -> b) -> b -> Product f g a -> b # foldl' :: (b -> a -> b) -> b -> Product f g a -> b # foldr1 :: (a -> a -> a) -> Product f g a -> a # foldl1 :: (a -> a -> a) -> Product f g a -> a # toList :: Product f g a -> [a] # null :: Product f g a -> Bool # length :: Product f g a -> Int # elem :: Eq a => a -> Product f g a -> Bool # maximum :: Ord a => Product f g a -> a # minimum :: Ord a => Product f g a -> a # sum :: Num a => Product f g a -> a # product :: Num a => Product f g a -> a #
(Foldable f, Foldable g) => Foldable (Sum f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Sum Methods fold :: Monoid m => Sum f g m -> m # foldMap :: Monoid m => (a -> m) -> Sum f g a -> m # foldMap' :: Monoid m => (a -> m) -> Sum f g a -> m # foldr :: (a -> b -> b) -> b -> Sum f g a -> b # foldr' :: (a -> b -> b) -> b -> Sum f g a -> b # foldl :: (b -> a -> b) -> b -> Sum f g a -> b # foldl' :: (b -> a -> b) -> b -> Sum f g a -> b # foldr1 :: (a -> a -> a) -> Sum f g a -> a # foldl1 :: (a -> a -> a) -> Sum f g a -> a # toList :: Sum f g a -> [a] # null :: Sum f g a -> Bool # length :: Sum f g a -> Int # elem :: Eq a => a -> Sum f g a -> Bool # maximum :: Ord a => Sum f g a -> a # minimum :: Ord a => Sum f g a -> a # sum :: Num a => Sum f g a -> a # product :: Num a => Sum f g a -> a #
(Foldable f, Foldable g) => Foldable (f :*: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => (f :*: g) m -> m # foldMap :: Monoid m => (a -> m) -> (f :*: g) a -> m # foldMap' :: Monoid m => (a -> m) -> (f :*: g) a -> m # foldr :: (a -> b -> b) -> b -> (f :*: g) a -> b # foldr' :: (a -> b -> b) -> b -> (f :*: g) a -> b # foldl :: (b -> a -> b) -> b -> (f :*: g) a -> b # foldl' :: (b -> a -> b) -> b -> (f :*: g) a -> b # foldr1 :: (a -> a -> a) -> (f :*: g) a -> a # foldl1 :: (a -> a -> a) -> (f :*: g) a -> a # toList :: (f :*: g) a -> [a] # null :: (f :*: g) a -> Bool # length :: (f :*: g) a -> Int # elem :: Eq a => a -> (f :*: g) a -> Bool # maximum :: Ord a => (f :*: g) a -> a # minimum :: Ord a => (f :*: g) a -> a # sum :: Num a => (f :*: g) a -> a # product :: Num a => (f :*: g) a -> a #
(Foldable f, Foldable g) => Foldable (f :+: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => (f :+: g) m -> m # foldMap :: Monoid m => (a -> m) -> (f :+: g) a -> m # foldMap' :: Monoid m => (a -> m) -> (f :+: g) a -> m # foldr :: (a -> b -> b) -> b -> (f :+: g) a -> b # foldr' :: (a -> b -> b) -> b -> (f :+: g) a -> b # foldl :: (b -> a -> b) -> b -> (f :+: g) a -> b # foldl' :: (b -> a -> b) -> b -> (f :+: g) a -> b # foldr1 :: (a -> a -> a) -> (f :+: g) a -> a # foldl1 :: (a -> a -> a) -> (f :+: g) a -> a # toList :: (f :+: g) a -> [a] # null :: (f :+: g) a -> Bool # length :: (f :+: g) a -> Int # elem :: Eq a => a -> (f :+: g) a -> Bool # maximum :: Ord a => (f :+: g) a -> a # minimum :: Ord a => (f :+: g) a -> a # sum :: Num a => (f :+: g) a -> a # product :: Num a => (f :+: g) a -> a #
Foldable (K1 i c :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => K1 i c m -> m # foldMap :: Monoid m => (a -> m) -> K1 i c a -> m # foldMap' :: Monoid m => (a -> m) -> K1 i c a -> m # foldr :: (a -> b -> b) -> b -> K1 i c a -> b # foldr' :: (a -> b -> b) -> b -> K1 i c a -> b # foldl :: (b -> a -> b) -> b -> K1 i c a -> b # foldl' :: (b -> a -> b) -> b -> K1 i c a -> b # foldr1 :: (a -> a -> a) -> K1 i c a -> a # foldl1 :: (a -> a -> a) -> K1 i c a -> a # toList :: K1 i c a -> [a] # null :: K1 i c a -> Bool # length :: K1 i c a -> Int # elem :: Eq a => a -> K1 i c a -> Bool # maximum :: Ord a => K1 i c a -> a # minimum :: Ord a => K1 i c a -> a # sum :: Num a => K1 i c a -> a # product :: Num a => K1 i c a -> a #
(Foldable f, Foldable g) => Foldable (Compose f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Compose Methods fold :: Monoid m => Compose f g m -> m # foldMap :: Monoid m => (a -> m) -> Compose f g a -> m # foldMap' :: Monoid m => (a -> m) -> Compose f g a -> m # foldr :: (a -> b -> b) -> b -> Compose f g a -> b # foldr' :: (a -> b -> b) -> b -> Compose f g a -> b # foldl :: (b -> a -> b) -> b -> Compose f g a -> b # foldl' :: (b -> a -> b) -> b -> Compose f g a -> b # foldr1 :: (a -> a -> a) -> Compose f g a -> a # foldl1 :: (a -> a -> a) -> Compose f g a -> a # toList :: Compose f g a -> [a] # null :: Compose f g a -> Bool # length :: Compose f g a -> Int # elem :: Eq a => a -> Compose f g a -> Bool # maximum :: Ord a => Compose f g a -> a # minimum :: Ord a => Compose f g a -> a # sum :: Num a => Compose f g a -> a # product :: Num a => Compose f g a -> a #
(Foldable f, Foldable g) => Foldable (f :.: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => (f :.: g) m -> m # foldMap :: Monoid m => (a -> m) -> (f :.: g) a -> m # foldMap' :: Monoid m => (a -> m) -> (f :.: g) a -> m # foldr :: (a -> b -> b) -> b -> (f :.: g) a -> b # foldr' :: (a -> b -> b) -> b -> (f :.: g) a -> b # foldl :: (b -> a -> b) -> b -> (f :.: g) a -> b # foldl' :: (b -> a -> b) -> b -> (f :.: g) a -> b # foldr1 :: (a -> a -> a) -> (f :.: g) a -> a # foldl1 :: (a -> a -> a) -> (f :.: g) a -> a # toList :: (f :.: g) a -> [a] # null :: (f :.: g) a -> Bool # length :: (f :.: g) a -> Int # elem :: Eq a => a -> (f :.: g) a -> Bool # maximum :: Ord a => (f :.: g) a -> a # minimum :: Ord a => (f :.: g) a -> a # sum :: Num a => (f :.: g) a -> a # product :: Num a => (f :.: g) a -> a #
Foldable f => Foldable (M1 i c f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => M1 i c f m -> m # foldMap :: Monoid m => (a -> m) -> M1 i c f a -> m # foldMap' :: Monoid m => (a -> m) -> M1 i c f a -> m # foldr :: (a -> b -> b) -> b -> M1 i c f a -> b # foldr' :: (a -> b -> b) -> b -> M1 i c f a -> b # foldl :: (b -> a -> b) -> b -> M1 i c f a -> b # foldl' :: (b -> a -> b) -> b -> M1 i c f a -> b # foldr1 :: (a -> a -> a) -> M1 i c f a -> a # foldl1 :: (a -> a -> a) -> M1 i c f a -> a # toList :: M1 i c f a -> [a] # null :: M1 i c f a -> Bool # length :: M1 i c f a -> Int # elem :: Eq a => a -> M1 i c f a -> Bool # maximum :: Ord a => M1 i c f a -> a # minimum :: Ord a => M1 i c f a -> a # sum :: Num a => M1 i c f a -> a # product :: Num a => M1 i c f a -> a #

elem :: (Foldable t, Eq a) => a -> t a -> Bool infix 4 #

Does the element occur in the structure?

Note: `elem` is often used in infix form.

#### Examples

Expand

Basic usage:

    >>> 3 `elem` []
    False

    >>> 3 `elem` [1,2]
    False

    >>> 3 `elem` [1,2,3,4,5]
    True

For infinite structures, the default implementation of `elem` terminates if the sought-after value exists at a finite distance from the left side of the structure:

    >>> 3 `elem` [1..]
    True

    >>> 3 `elem` ([4..] ++ [3])
    * Hangs forever *

@since base-4.8.0.0

maximum :: (Foldable t, Ord a) => t a -> a #

The largest element of a non-empty structure.

This function is non-total and will raise a runtime exception if the structure happens to be empty. A structure that supports random access and maintains its elements in order should provide a specialised implementation to return the maximum in faster than linear time.

#### Examples

Expand

Basic usage:

    >>> maximum [1..10]
    10

    >>> maximum []
    *** Exception: Prelude.maximum: empty list

    >>> maximum Nothing
    *** Exception: maximum: empty structure

WARNING: This function is partial for possibly-empty structures like lists.

@since base-4.8.0.0

minimum :: (Foldable t, Ord a) => t a -> a #

The least element of a non-empty structure.

This function is non-total and will raise a runtime exception if the structure happens to be empty. A structure that supports random access and maintains its elements in order should provide a specialised implementation to return the minimum in faster than linear time.

#### Examples

Expand

Basic usage:

    >>> minimum [1..10]
    1

    >>> minimum []
    *** Exception: Prelude.minimum: empty list

    >>> minimum Nothing
    *** Exception: minimum: empty structure

WARNING: This function is partial for possibly-empty structures like lists.

@since base-4.8.0.0

traverse_ :: (Foldable t, Applicative f) => (a -> f b) -> t a -> f () #

Map each element of a structure to an `Applicative` action, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results see `traverse`.

`traverse_` is just like `mapM_`, but generalised to `Applicative` actions.

#### Examples

Expand

Basic usage:

    >>> traverse_ print ["Hello", "world", "!"]
    "Hello"
    "world"
    "!"

sequenceA_ :: (Foldable t, Applicative f) => t (f a) -> f () #

Evaluate each action in the structure from left to right, and ignore the results. For a version that doesn't ignore the results see `sequenceA`.

`sequenceA_` is just like `sequence_`, but generalised to `Applicative` actions.

#### Examples

Expand

Basic usage:

    >>> sequenceA_ [print "Hello", print "world", print "!"]
    "Hello"
    "world"
    "!"

for_ :: (Foldable t, Applicative f) => t a -> (a -> f b) -> f () #

`for_` is `traverse_` with its arguments flipped. For a version that doesn't ignore the results see `for`. This is `forM_` generalised to `Applicative` actions.

`for_` is just like `forM_`, but generalised to `Applicative` actions.

#### Examples

Expand

Basic usage:

    >>> for_ [1..4] print
    1
    2
    3
    4

maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a #

The largest element of a non-empty structure with respect to the given comparison function.

#### Examples

Expand

Basic usage:

    >>> maximumBy (compare `on` length) ["Hello", "World", "!", "Longest", "bar"]
    "Longest"

WARNING: This function is partial for possibly-empty structures like lists.

minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a #

The least element of a non-empty structure with respect to the given comparison function.

#### Examples

Expand

Basic usage:

    >>> minimumBy (compare `on` length) ["Hello", "World", "!", "Longest", "bar"]
    "!"

WARNING: This function is partial for possibly-empty structures like lists.

class (Functor t, Foldable t) => Traversable (t :: Type -> Type) where #

Functors representing data structures that can be transformed to structures of the same shape by performing an `Applicative` (or, therefore, `Monad`) action on each element from left to right.

A more detailed description of what same shape means, the various methods, how traversals are constructed, and example advanced use-cases can be found in the Overview section of Data.Traversable.

For the class laws see the Laws section of Data.Traversable.

Minimal complete definition

traverse | sequenceA

Methods

traverse :: Applicative f => (a -> f b) -> t a -> f (t b) #

Map each element of a structure to an action, evaluate these actions from left to right, and collect the results. For a version that ignores the results see `traverse_`.

#### Examples

Expand

Basic usage:

In the first two examples we show each evaluated action mapping to the output structure.

    >>> traverse Just [1,2,3,4]
    Just [1,2,3,4]

    >>> traverse id [Right 1, Right 2, Right 3, Right 4]
    Right [1,2,3,4]

In the next examples, we show that `Nothing` and `Left` values short circuit the created structure.

    >>> traverse (const Nothing) [1,2,3,4]
    Nothing

    >>> traverse (\x -> if odd x then Just x else Nothing)  [1,2,3,4]
    Nothing

    >>> traverse id [Right 1, Right 2, Right 3, Right 4, Left 0]
    Left 0

sequenceA :: Applicative f => t (f a) -> f (t a) #

Evaluate each action in the structure from left to right, and collect the results. For a version that ignores the results see `sequenceA_`.

#### Examples

Expand

Basic usage:

For the first two examples we show sequenceA fully evaluating a a structure and collecting the results.

    >>> sequenceA [Just 1, Just 2, Just 3]
    Just [1,2,3]

    >>> sequenceA [Right 1, Right 2, Right 3]
    Right [1,2,3]

The next two example show `Nothing` and `Just` will short circuit the resulting structure if present in the input. For more context, check the `Traversable` instances for `Either` and `Maybe`.

    >>> sequenceA [Just 1, Just 2, Just 3, Nothing]
    Nothing

    >>> sequenceA [Right 1, Right 2, Right 3, Left 4]
    Left 4

mapM :: Monad m => (a -> m b) -> t a -> m (t b) #

Map each element of a structure to a monadic action, evaluate these actions from left to right, and collect the results. For a version that ignores the results see `mapM_`.

#### Examples

Expand

`mapM` is literally a `traverse` with a type signature restricted to `Monad`. Its implementation may be more efficient due to additional power of `Monad`.

sequence :: Monad m => t (m a) -> m (t a) #

Evaluate each monadic action in the structure from left to right, and collect the results. For a version that ignores the results see `sequence_`.

#### Examples

Expand

Basic usage:

The first two examples are instances where the input and and output of `sequence` are isomorphic.

    >>> sequence $ Right [1,2,3,4]
    [Right 1,Right 2,Right 3,Right 4]

    >>> sequence $ [Right 1,Right 2,Right 3,Right 4]
    Right [1,2,3,4]

The following examples demonstrate short circuit behavior for `sequence`.

    >>> sequence $ Left [1,2,3,4]
    Left [1,2,3,4]

    >>> sequence $ [Left 0, Right 1,Right 2,Right 3,Right 4]
    Left 0

#### Instances

Instances details

Traversable Complex | Since: base-4.9.0.0
Instance details Defined in Data.Complex Methods traverse :: Applicative f => (a -> f b) -> Complex a -> f (Complex b) # sequenceA :: Applicative f => Complex (f a) -> f (Complex a) # mapM :: Monad m => (a -> m b) -> Complex a -> m (Complex b) # sequence :: Monad m => Complex (m a) -> m (Complex a) #
Traversable First | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods traverse :: Applicative f => (a -> f b) -> First a -> f (First b) # sequenceA :: Applicative f => First (f a) -> f (First a) # mapM :: Monad m => (a -> m b) -> First a -> m (First b) # sequence :: Monad m => First (m a) -> m (First a) #
Traversable Last | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods traverse :: Applicative f => (a -> f b) -> Last a -> f (Last b) # sequenceA :: Applicative f => Last (f a) -> f (Last a) # mapM :: Monad m => (a -> m b) -> Last a -> m (Last b) # sequence :: Monad m => Last (m a) -> m (Last a) #
Traversable Max | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods traverse :: Applicative f => (a -> f b) -> Max a -> f (Max b) # sequenceA :: Applicative f => Max (f a) -> f (Max a) # mapM :: Monad m => (a -> m b) -> Max a -> m (Max b) # sequence :: Monad m => Max (m a) -> m (Max a) #
Traversable Min | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods traverse :: Applicative f => (a -> f b) -> Min a -> f (Min b) # sequenceA :: Applicative f => Min (f a) -> f (Min a) # mapM :: Monad m => (a -> m b) -> Min a -> m (Min b) # sequence :: Monad m => Min (m a) -> m (Min a) #
Traversable SCC | Since: containers-0.5.9
Instance details Defined in Data.Graph Methods traverse :: Applicative f => (a -> f b) -> SCC a -> f (SCC b) # sequenceA :: Applicative f => SCC (f a) -> f (SCC a) # mapM :: Monad m => (a -> m b) -> SCC a -> m (SCC b) # sequence :: Monad m => SCC (m a) -> m (SCC a) #
Traversable IntMap | Traverses in order of increasing key.
Instance details Defined in Data.IntMap.Internal Methods traverse :: Applicative f => (a -> f b) -> IntMap a -> f (IntMap b) # sequenceA :: Applicative f => IntMap (f a) -> f (IntMap a) # mapM :: Monad m => (a -> m b) -> IntMap a -> m (IntMap b) # sequence :: Monad m => IntMap (m a) -> m (IntMap a) #
Traversable Digit |
Instance details Defined in Data.Sequence.Internal Methods traverse :: Applicative f => (a -> f b) -> Digit a -> f (Digit b) # sequenceA :: Applicative f => Digit (f a) -> f (Digit a) # mapM :: Monad m => (a -> m b) -> Digit a -> m (Digit b) # sequence :: Monad m => Digit (m a) -> m (Digit a) #
Traversable Elem |
Instance details Defined in Data.Sequence.Internal Methods traverse :: Applicative f => (a -> f b) -> Elem a -> f (Elem b) # sequenceA :: Applicative f => Elem (f a) -> f (Elem a) # mapM :: Monad m => (a -> m b) -> Elem a -> m (Elem b) # sequence :: Monad m => Elem (m a) -> m (Elem a) #
Traversable FingerTree |
Instance details Defined in Data.Sequence.Internal Methods traverse :: Applicative f => (a -> f b) -> FingerTree a -> f (FingerTree b) # sequenceA :: Applicative f => FingerTree (f a) -> f (FingerTree a) # mapM :: Monad m => (a -> m b) -> FingerTree a -> m (FingerTree b) # sequence :: Monad m => FingerTree (m a) -> m (FingerTree a) #
Traversable Node |
Instance details Defined in Data.Sequence.Internal Methods traverse :: Applicative f => (a -> f b) -> Node a -> f (Node b) # sequenceA :: Applicative f => Node (f a) -> f (Node a) # mapM :: Monad m => (a -> m b) -> Node a -> m (Node b) # sequence :: Monad m => Node (m a) -> m (Node a) #
Traversable Seq |
Instance details Defined in Data.Sequence.Internal Methods traverse :: Applicative f => (a -> f b) -> Seq a -> f (Seq b) # sequenceA :: Applicative f => Seq (f a) -> f (Seq a) # mapM :: Monad m => (a -> m b) -> Seq a -> m (Seq b) # sequence :: Monad m => Seq (m a) -> m (Seq a) #
Traversable ViewL |
Instance details Defined in Data.Sequence.Internal Methods traverse :: Applicative f => (a -> f b) -> ViewL a -> f (ViewL b) # sequenceA :: Applicative f => ViewL (f a) -> f (ViewL a) # mapM :: Monad m => (a -> m b) -> ViewL a -> m (ViewL b) # sequence :: Monad m => ViewL (m a) -> m (ViewL a) #
Traversable ViewR |
Instance details Defined in Data.Sequence.Internal Methods traverse :: Applicative f => (a -> f b) -> ViewR a -> f (ViewR b) # sequenceA :: Applicative f => ViewR (f a) -> f (ViewR a) # mapM :: Monad m => (a -> m b) -> ViewR a -> m (ViewR b) # sequence :: Monad m => ViewR (m a) -> m (ViewR a) #
Traversable Tree |
Instance details Defined in Data.Tree Methods traverse :: Applicative f => (a -> f b) -> Tree a -> f (Tree b) # sequenceA :: Applicative f => Tree (f a) -> f (Tree a) # mapM :: Monad m => (a -> m b) -> Tree a -> m (Tree b) # sequence :: Monad m => Tree (m a) -> m (Tree a) #
Traversable NonEmpty | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> NonEmpty a -> f (NonEmpty b) # sequenceA :: Applicative f => NonEmpty (f a) -> f (NonEmpty a) # mapM :: Monad m => (a -> m b) -> NonEmpty a -> m (NonEmpty b) # sequence :: Monad m => NonEmpty (m a) -> m (NonEmpty a) #
Traversable Identity | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Identity a -> f (Identity b) # sequenceA :: Applicative f => Identity (f a) -> f (Identity a) # mapM :: Monad m => (a -> m b) -> Identity a -> m (Identity b) # sequence :: Monad m => Identity (m a) -> m (Identity a) #
Traversable First | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> First a -> f (First b) # sequenceA :: Applicative f => First (f a) -> f (First a) # mapM :: Monad m => (a -> m b) -> First a -> m (First b) # sequence :: Monad m => First (m a) -> m (First a) #
Traversable Last | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Last a -> f (Last b) # sequenceA :: Applicative f => Last (f a) -> f (Last a) # mapM :: Monad m => (a -> m b) -> Last a -> m (Last b) # sequence :: Monad m => Last (m a) -> m (Last a) #
Traversable Down | @since base-4.12.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Down a -> f (Down b) # sequenceA :: Applicative f => Down (f a) -> f (Down a) # mapM :: Monad m => (a -> m b) -> Down a -> m (Down b) # sequence :: Monad m => Down (m a) -> m (Down a) #
Traversable Dual | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Dual a -> f (Dual b) # sequenceA :: Applicative f => Dual (f a) -> f (Dual a) # mapM :: Monad m => (a -> m b) -> Dual a -> m (Dual b) # sequence :: Monad m => Dual (m a) -> m (Dual a) #
Traversable Product | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Product a -> f (Product b) # sequenceA :: Applicative f => Product (f a) -> f (Product a) # mapM :: Monad m => (a -> m b) -> Product a -> m (Product b) # sequence :: Monad m => Product (m a) -> m (Product a) #
Traversable Sum | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Sum a -> f (Sum b) # sequenceA :: Applicative f => Sum (f a) -> f (Sum a) # mapM :: Monad m => (a -> m b) -> Sum a -> m (Sum b) # sequence :: Monad m => Sum (m a) -> m (Sum a) #
Traversable Par1 | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Par1 a -> f (Par1 b) # sequenceA :: Applicative f => Par1 (f a) -> f (Par1 a) # mapM :: Monad m => (a -> m b) -> Par1 a -> m (Par1 b) # sequence :: Monad m => Par1 (m a) -> m (Par1 a) #
Traversable Array |
Instance details Defined in Data.Primitive.Array Methods traverse :: Applicative f => (a -> f b) -> Array a -> f (Array b) # sequenceA :: Applicative f => Array (f a) -> f (Array a) # mapM :: Monad m => (a -> m b) -> Array a -> m (Array b) # sequence :: Monad m => Array (m a) -> m (Array a) #
Traversable SmallArray |
Instance details Defined in Data.Primitive.SmallArray Methods traverse :: Applicative f => (a -> f b) -> SmallArray a -> f (SmallArray b) # sequenceA :: Applicative f => SmallArray (f a) -> f (SmallArray a) # mapM :: Monad m => (a -> m b) -> SmallArray a -> m (SmallArray b) # sequence :: Monad m => SmallArray (m a) -> m (SmallArray a) #
Traversable Vector |
Instance details Defined in Data.Vector Methods traverse :: Applicative f => (a -> f b) -> Vector a -> f (Vector b) # sequenceA :: Applicative f => Vector (f a) -> f (Vector a) # mapM :: Monad m => (a -> m b) -> Vector a -> m (Vector b) # sequence :: Monad m => Vector (m a) -> m (Vector a) #
Traversable Vector |
Instance details Defined in Data.Vector.Strict Methods traverse :: Applicative f => (a -> f b) -> Vector a -> f (Vector b) # sequenceA :: Applicative f => Vector (f a) -> f (Vector a) # mapM :: Monad m => (a -> m b) -> Vector a -> m (Vector b) # sequence :: Monad m => Vector (m a) -> m (Vector a) #
Traversable Maybe | @since base-2.01
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Maybe a -> f (Maybe b) # sequenceA :: Applicative f => Maybe (f a) -> f (Maybe a) # mapM :: Monad m => (a -> m b) -> Maybe a -> m (Maybe b) # sequence :: Monad m => Maybe (m a) -> m (Maybe a) #
Traversable Solo | @since base-4.15
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Solo a -> f (Solo b) # sequenceA :: Applicative f => Solo (f a) -> f (Solo a) # mapM :: Monad m => (a -> m b) -> Solo a -> m (Solo b) # sequence :: Monad m => Solo (m a) -> m (Solo a) #
Traversable [] | @since base-2.01
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> [a] -> f [b] # sequenceA :: Applicative f => [f a] -> f [a] # mapM :: Monad m => (a -> m b) -> [a] -> m [b] # sequence :: Monad m => [m a] -> m [a] #
Traversable (Arg a) | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods traverse :: Applicative f => (a0 -> f b) -> Arg a a0 -> f (Arg a b) # sequenceA :: Applicative f => Arg a (f a0) -> f (Arg a a0) # mapM :: Monad m => (a0 -> m b) -> Arg a a0 -> m (Arg a b) # sequence :: Monad m => Arg a (m a0) -> m (Arg a a0) #
Traversable (Map k) | Traverses in order of increasing key.
Instance details Defined in Data.Map.Internal Methods traverse :: Applicative f => (a -> f b) -> Map k a -> f (Map k b) # sequenceA :: Applicative f => Map k (f a) -> f (Map k a) # mapM :: Monad m => (a -> m b) -> Map k a -> m (Map k b) # sequence :: Monad m => Map k (m a) -> m (Map k a) #
Ix i => Traversable (Array i) | @since base-2.01
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Array i a -> f (Array i b) # sequenceA :: Applicative f => Array i (f a) -> f (Array i a) # mapM :: Monad m => (a -> m b) -> Array i a -> m (Array i b) # sequence :: Monad m => Array i (m a) -> m (Array i a) #
Traversable (Either a) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a0 -> f b) -> Either a a0 -> f (Either a b) # sequenceA :: Applicative f => Either a (f a0) -> f (Either a a0) # mapM :: Monad m => (a0 -> m b) -> Either a a0 -> m (Either a b) # sequence :: Monad m => Either a (m a0) -> m (Either a a0) #
Traversable (Proxy :: Type -> Type) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Proxy a -> f (Proxy b) # sequenceA :: Applicative f => Proxy (f a) -> f (Proxy a) # mapM :: Monad m => (a -> m b) -> Proxy a -> m (Proxy b) # sequence :: Monad m => Proxy (m a) -> m (Proxy a) #
Traversable (U1 :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> U1 a -> f (U1 b) # sequenceA :: Applicative f => U1 (f a) -> f (U1 a) # mapM :: Monad m => (a -> m b) -> U1 a -> m (U1 b) # sequence :: Monad m => U1 (m a) -> m (U1 a) #
Traversable (UAddr :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> UAddr a -> f (UAddr b) # sequenceA :: Applicative f => UAddr (f a) -> f (UAddr a) # mapM :: Monad m => (a -> m b) -> UAddr a -> m (UAddr b) # sequence :: Monad m => UAddr (m a) -> m (UAddr a) #
Traversable (UChar :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> UChar a -> f (UChar b) # sequenceA :: Applicative f => UChar (f a) -> f (UChar a) # mapM :: Monad m => (a -> m b) -> UChar a -> m (UChar b) # sequence :: Monad m => UChar (m a) -> m (UChar a) #
Traversable (UDouble :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> UDouble a -> f (UDouble b) # sequenceA :: Applicative f => UDouble (f a) -> f (UDouble a) # mapM :: Monad m => (a -> m b) -> UDouble a -> m (UDouble b) # sequence :: Monad m => UDouble (m a) -> m (UDouble a) #
Traversable (UFloat :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> UFloat a -> f (UFloat b) # sequenceA :: Applicative f => UFloat (f a) -> f (UFloat a) # mapM :: Monad m => (a -> m b) -> UFloat a -> m (UFloat b) # sequence :: Monad m => UFloat (m a) -> m (UFloat a) #
Traversable (UInt :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> UInt a -> f (UInt b) # sequenceA :: Applicative f => UInt (f a) -> f (UInt a) # mapM :: Monad m => (a -> m b) -> UInt a -> m (UInt b) # sequence :: Monad m => UInt (m a) -> m (UInt a) #
Traversable (UWord :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> UWord a -> f (UWord b) # sequenceA :: Applicative f => UWord (f a) -> f (UWord a) # mapM :: Monad m => (a -> m b) -> UWord a -> m (UWord b) # sequence :: Monad m => UWord (m a) -> m (UWord a) #
Traversable (V1 :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> V1 a -> f (V1 b) # sequenceA :: Applicative f => V1 (f a) -> f (V1 a) # mapM :: Monad m => (a -> m b) -> V1 a -> m (V1 b) # sequence :: Monad m => V1 (m a) -> m (V1 a) #
Traversable f => Traversable (Lift f) |
Instance details Defined in Control.Applicative.Lift Methods traverse :: Applicative f0 => (a -> f0 b) -> Lift f a -> f0 (Lift f b) # sequenceA :: Applicative f0 => Lift f (f0 a) -> f0 (Lift f a) # mapM :: Monad m => (a -> m b) -> Lift f a -> m (Lift f b) # sequence :: Monad m => Lift f (m a) -> m (Lift f a) #
Traversable f => Traversable (MaybeT f) |
Instance details Defined in Control.Monad.Trans.Maybe Methods traverse :: Applicative f0 => (a -> f0 b) -> MaybeT f a -> f0 (MaybeT f b) # sequenceA :: Applicative f0 => MaybeT f (f0 a) -> f0 (MaybeT f a) # mapM :: Monad m => (a -> m b) -> MaybeT f a -> m (MaybeT f b) # sequence :: Monad m => MaybeT f (m a) -> m (MaybeT f a) #
Traversable (HashMap k) |
Instance details Defined in Data.HashMap.Internal Methods traverse :: Applicative f => (a -> f b) -> HashMap k a -> f (HashMap k b) # sequenceA :: Applicative f => HashMap k (f a) -> f (HashMap k a) # mapM :: Monad m => (a -> m b) -> HashMap k a -> m (HashMap k b) # sequence :: Monad m => HashMap k (m a) -> m (HashMap k a) #
Traversable ((,) a) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a0 -> f b) -> (a, a0) -> f (a, b) # sequenceA :: Applicative f => (a, f a0) -> f (a, a0) # mapM :: Monad m => (a0 -> m b) -> (a, a0) -> m (a, b) # sequence :: Monad m => (a, m a0) -> m (a, a0) #
Traversable (Const m :: Type -> Type) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> Const m a -> f (Const m b) # sequenceA :: Applicative f => Const m (f a) -> f (Const m a) # mapM :: Monad m0 => (a -> m0 b) -> Const m a -> m0 (Const m b) # sequence :: Monad m0 => Const m (m0 a) -> m0 (Const m a) #
Traversable f => Traversable (Ap f) | @since base-4.12.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f0 => (a -> f0 b) -> Ap f a -> f0 (Ap f b) # sequenceA :: Applicative f0 => Ap f (f0 a) -> f0 (Ap f a) # mapM :: Monad m => (a -> m b) -> Ap f a -> m (Ap f b) # sequence :: Monad m => Ap f (m a) -> m (Ap f a) #
Traversable f => Traversable (Alt f) | @since base-4.12.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f0 => (a -> f0 b) -> Alt f a -> f0 (Alt f b) # sequenceA :: Applicative f0 => Alt f (f0 a) -> f0 (Alt f a) # mapM :: Monad m => (a -> m b) -> Alt f a -> m (Alt f b) # sequence :: Monad m => Alt f (m a) -> m (Alt f a) #
Traversable f => Traversable (Rec1 f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f0 => (a -> f0 b) -> Rec1 f a -> f0 (Rec1 f b) # sequenceA :: Applicative f0 => Rec1 f (f0 a) -> f0 (Rec1 f a) # mapM :: Monad m => (a -> m b) -> Rec1 f a -> m (Rec1 f b) # sequence :: Monad m => Rec1 f (m a) -> m (Rec1 f a) #
Traversable f => Traversable (Backwards f) | Derived instance.
Instance details Defined in Control.Applicative.Backwards Methods traverse :: Applicative f0 => (a -> f0 b) -> Backwards f a -> f0 (Backwards f b) # sequenceA :: Applicative f0 => Backwards f (f0 a) -> f0 (Backwards f a) # mapM :: Monad m => (a -> m b) -> Backwards f a -> m (Backwards f b) # sequence :: Monad m => Backwards f (m a) -> m (Backwards f a) #
Traversable f => Traversable (ExceptT e f) |
Instance details Defined in Control.Monad.Trans.Except Methods traverse :: Applicative f0 => (a -> f0 b) -> ExceptT e f a -> f0 (ExceptT e f b) # sequenceA :: Applicative f0 => ExceptT e f (f0 a) -> f0 (ExceptT e f a) # mapM :: Monad m => (a -> m b) -> ExceptT e f a -> m (ExceptT e f b) # sequence :: Monad m => ExceptT e f (m a) -> m (ExceptT e f a) #
Traversable f => Traversable (IdentityT f) |
Instance details Defined in Control.Monad.Trans.Identity Methods traverse :: Applicative f0 => (a -> f0 b) -> IdentityT f a -> f0 (IdentityT f b) # sequenceA :: Applicative f0 => IdentityT f (f0 a) -> f0 (IdentityT f a) # mapM :: Monad m => (a -> m b) -> IdentityT f a -> m (IdentityT f b) # sequence :: Monad m => IdentityT f (m a) -> m (IdentityT f a) #
Traversable f => Traversable (WriterT w f) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods traverse :: Applicative f0 => (a -> f0 b) -> WriterT w f a -> f0 (WriterT w f b) # sequenceA :: Applicative f0 => WriterT w f (f0 a) -> f0 (WriterT w f a) # mapM :: Monad m => (a -> m b) -> WriterT w f a -> m (WriterT w f b) # sequence :: Monad m => WriterT w f (m a) -> m (WriterT w f a) #
Traversable f => Traversable (WriterT w f) |
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods traverse :: Applicative f0 => (a -> f0 b) -> WriterT w f a -> f0 (WriterT w f b) # sequenceA :: Applicative f0 => WriterT w f (f0 a) -> f0 (WriterT w f a) # mapM :: Monad m => (a -> m b) -> WriterT w f a -> m (WriterT w f b) # sequence :: Monad m => WriterT w f (m a) -> m (WriterT w f a) #
Traversable (Constant a :: Type -> Type) |
Instance details Defined in Data.Functor.Constant Methods traverse :: Applicative f => (a0 -> f b) -> Constant a a0 -> f (Constant a b) # sequenceA :: Applicative f => Constant a (f a0) -> f (Constant a a0) # mapM :: Monad m => (a0 -> m b) -> Constant a a0 -> m (Constant a b) # sequence :: Monad m => Constant a (m a0) -> m (Constant a a0) #
Traversable f => Traversable (Reverse f) | Traverse from right to left.
Instance details Defined in Data.Functor.Reverse Methods traverse :: Applicative f0 => (a -> f0 b) -> Reverse f a -> f0 (Reverse f b) # sequenceA :: Applicative f0 => Reverse f (f0 a) -> f0 (Reverse f a) # mapM :: Monad m => (a -> m b) -> Reverse f a -> m (Reverse f b) # sequence :: Monad m => Reverse f (m a) -> m (Reverse f a) #
(Traversable f, Traversable g) => Traversable (Product f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Product Methods traverse :: Applicative f0 => (a -> f0 b) -> Product f g a -> f0 (Product f g b) # sequenceA :: Applicative f0 => Product f g (f0 a) -> f0 (Product f g a) # mapM :: Monad m => (a -> m b) -> Product f g a -> m (Product f g b) # sequence :: Monad m => Product f g (m a) -> m (Product f g a) #
(Traversable f, Traversable g) => Traversable (Sum f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Sum Methods traverse :: Applicative f0 => (a -> f0 b) -> Sum f g a -> f0 (Sum f g b) # sequenceA :: Applicative f0 => Sum f g (f0 a) -> f0 (Sum f g a) # mapM :: Monad m => (a -> m b) -> Sum f g a -> m (Sum f g b) # sequence :: Monad m => Sum f g (m a) -> m (Sum f g a) #
(Traversable f, Traversable g) => Traversable (f :*: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f0 => (a -> f0 b) -> (f :*: g) a -> f0 ((f :*: g) b) # sequenceA :: Applicative f0 => (f :*: g) (f0 a) -> f0 ((f :*: g) a) # mapM :: Monad m => (a -> m b) -> (f :*: g) a -> m ((f :*: g) b) # sequence :: Monad m => (f :*: g) (m a) -> m ((f :*: g) a) #
(Traversable f, Traversable g) => Traversable (f :+: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f0 => (a -> f0 b) -> (f :+: g) a -> f0 ((f :+: g) b) # sequenceA :: Applicative f0 => (f :+: g) (f0 a) -> f0 ((f :+: g) a) # mapM :: Monad m => (a -> m b) -> (f :+: g) a -> m ((f :+: g) b) # sequence :: Monad m => (f :+: g) (m a) -> m ((f :+: g) a) #
Traversable (K1 i c :: Type -> Type) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> K1 i c a -> f (K1 i c b) # sequenceA :: Applicative f => K1 i c (f a) -> f (K1 i c a) # mapM :: Monad m => (a -> m b) -> K1 i c a -> m (K1 i c b) # sequence :: Monad m => K1 i c (m a) -> m (K1 i c a) #
(Traversable f, Traversable g) => Traversable (Compose f g) | Since: base-4.9.0.0
Instance details Defined in Data.Functor.Compose Methods traverse :: Applicative f0 => (a -> f0 b) -> Compose f g a -> f0 (Compose f g b) # sequenceA :: Applicative f0 => Compose f g (f0 a) -> f0 (Compose f g a) # mapM :: Monad m => (a -> m b) -> Compose f g a -> m (Compose f g b) # sequence :: Monad m => Compose f g (m a) -> m (Compose f g a) #
(Traversable f, Traversable g) => Traversable (f :.: g) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f0 => (a -> f0 b) -> (f :.: g) a -> f0 ((f :.: g) b) # sequenceA :: Applicative f0 => (f :.: g) (f0 a) -> f0 ((f :.: g) a) # mapM :: Monad m => (a -> m b) -> (f :.: g) a -> m ((f :.: g) b) # sequence :: Monad m => (f :.: g) (m a) -> m ((f :.: g) a) #
Traversable f => Traversable (M1 i c f) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f0 => (a -> f0 b) -> M1 i c f a -> f0 (M1 i c f b) # sequenceA :: Applicative f0 => M1 i c f (f0 a) -> f0 (M1 i c f a) # mapM :: Monad m => (a -> m b) -> M1 i c f a -> m (M1 i c f b) # sequence :: Monad m => M1 i c f (m a) -> m (M1 i c f a) #

for :: (Traversable t, Applicative f) => t a -> (a -> f b) -> f (t b) #

`for` is `traverse` with its arguments flipped. For a version that ignores the results see `for_`.

# Enhanced exports

## Simpler name for a typeclassed operation

map :: Functor f => (a -> b) -> f a -> f b #

    map = fmap

empty :: Monoid w => w #

Deprecated: Use mempty

    empty = mempty

(++) :: Monoid w => w -> w -> w infixr 5 #

    (++) = mappend

concat :: Monoid w => [w] -> w #

    concat = mconcat

intercalate :: Monoid w => w -> [w] -> w #

    intercalate = mconcat .: intersperse

## Strict implementation

sum :: (Foldable f, Num a) => f a -> a #

Compute the sum of a finite list of numbers.

product :: (Foldable f, Num a) => f a -> a #

Compute the product of a finite list of numbers.

## Text for Read and Show operations

tshow :: Show a => a -> Text #

Convert a value to readable Text

Since: 0.6.0

fromShow :: (Show a, IsString b) => a -> b #

Convert a value to readable IsString

Since 0.3.12

read :: Read a => Text -> a #

Parse Text to a value

readIO :: (MonadIO m, Read a) => Text -> m a #

The readIO function is similar to read except that it signals parse failure to the IO monad instead of terminating the program.

Since: 0.7.0

## FilePath for file operations

readFile :: MonadIO m => FilePath -> m Text #

Read a file and return the contents of the file as Text. The entire file is read strictly.

Since: 0.7.0

writeFile :: MonadIO m => FilePath -> Text -> m () #

Write Text to a file. The file is truncated to zero length before writing begins.

Since: 0.7.0

appendFile :: MonadIO m => FilePath -> Text -> m () #

Write Text to the end of a file.

Since: 0.7.0

# Text exports

## Text operations (Pure)

lines :: Text -> [Text] #

O(n) Breaks a `Text` up into a list of `Text`s at newline characters `'\n'` (LF, line feed). The resulting strings do not contain newlines.

`lines` does not treat `'\r'` (CR, carriage return) as a newline character.

words :: Text -> [Text] #

O(n) Breaks a `Text` up into a list of words, delimited by `Char`s representing white space.

unlines :: [Text] -> Text #

O(n) Joins lines, after appending a terminating newline to each.

unwords :: [Text] -> Text #

O(n) Joins words using single space characters.

textToString :: Text -> String #

ltextToString :: LText -> String #

fpToText :: FilePath -> Text #

Deprecated: Use Data.Text.pack

This function assumes file paths are encoded in UTF8. If it cannot decode the `FilePath`, the result is just an approximation.

Since 0.3.13

fpFromText :: Text -> FilePath #

Deprecated: Use Data.Text.unpack

Since 0.3.13

fpToString :: FilePath -> String #

Deprecated: Use id

Since 0.3.13

encodeUtf8 :: Text -> ByteString #

Encode text using UTF-8 encoding.

decodeUtf8 :: ByteString -> Text #

Note that this is not the standard `Data.Text.Encoding.decodeUtf8`. That function will throw impure exceptions on any decoding errors. This function instead uses `decodeLenient`.

## Text operations (IO)

getLine :: MonadIO m => m Text #

Since: 0.7.0

getContents :: MonadIO m => m LText #

Since: 0.7.0

interact :: MonadIO m => (LText -> LText) -> m () #

Since: 0.7.0

# Miscellaneous prelude re-exports

## Math

gcd :: Integral a => a -> a -> a #

``gcd` x y` is the non-negative factor of both `x` and `y` of which every common factor of `x` and `y` is also a factor; for example ``gcd` 4 2 = 2`, ``gcd` (-4) 6 = 2`, ``gcd` 0 4` = `4`. ``gcd` 0 0` = `0`. (That is, the common divisor that is "greatest" in the divisibility preordering.)

Note: Since for signed fixed-width integer types, ``abs` `minBound` < 0`, the result may be negative if one of the arguments is ``minBound`` (and necessarily is if the other is `0` or ``minBound``) for such types.

lcm :: Integral a => a -> a -> a #

``lcm` x y` is the smallest positive integer that both `x` and `y` divide.

## Show and Read

class Show a where #

Conversion of values to readable `String`s.

Derived instances of `Show` have the following properties, which are compatible with derived instances of `Read`:

- The result of `show` is a syntactically correct Haskell expression containing only constants, given the fixity declarations in force at the point where the type is declared. It contains only the constructor names defined in the data type, parentheses, and spaces. When labelled constructor fields are used, braces, commas, field names, and equal signs are also used.
- If the constructor is defined to be an infix operator, then `showsPrec` will produce infix applications of the constructor.
- the representation will be enclosed in parentheses if the precedence of the top-level constructor in `x` is less than `d` (associativity is ignored). Thus, if `d` is `0` then the result is never surrounded in parentheses; if `d` is `11` it is always surrounded in parentheses, unless it is an atomic expression.
- If the constructor is defined using record syntax, then `show` will produce the record-syntax form, with the fields given in the same order as the original declaration.

For example, given the declarations

    infixr 5 :^:
    data Tree a =  Leaf a  |  Tree a :^: Tree a

the derived instance of `Show` is equivalent to

    instance (Show a) => Show (Tree a) where

           showsPrec d (Leaf m) = showParen (d > app_prec) $
                showString "Leaf " . showsPrec (app_prec+1) m
             where app_prec = 10

           showsPrec d (u :^: v) = showParen (d > up_prec) $
                showsPrec (up_prec+1) u .
                showString " :^: "      .
                showsPrec (up_prec+1) v
             where up_prec = 5

Note that right-associativity of `:^:` is ignored. For example,

- ``show` (Leaf 1 :^: Leaf 2 :^: Leaf 3)` produces the string `"Leaf 1 :^: (Leaf 2 :^: Leaf 3)"`.

Minimal complete definition

showsPrec | show

Methods

showsPrec #

Arguments

:: Int | the operator precedence of the enclosing context (a number from `0` to `11`). Function application has precedence `10`.
-> a | the value to be converted to a `String`
-> ShowS |

Convert a value to a readable `String`.

`showsPrec` should satisfy the law

    showsPrec d x r ++ s  ==  showsPrec d x (r ++ s)

Derived instances of `Read` and `Show` satisfy the following:

- `(x,"")` is an element of `(`readsPrec` d (`showsPrec` d x ""))`.

That is, `readsPrec` parses the string produced by `showsPrec`, and delivers the value that `showsPrec` started with.

show :: a -> String #

A specialised variant of `showsPrec`, using precedence context zero, and returning an ordinary `String`.

showList :: [a] -> ShowS #

The method `showList` is provided to allow the programmer to give a specialised way of showing lists of values. For example, this is used by the predefined `Show` instance of the `Char` type, where values of type `String` should be shown in double quotes, rather than between square brackets.

#### Instances

Instances details

Show ByteArray | Since: base-4.17.0.0
Instance details Defined in Data.Array.Byte Methods showsPrec :: Int -> ByteArray -> ShowS # show :: ByteArray -> String # showList :: [ByteArray] -> ShowS #
Show Timeout | Since: base-4.0
Instance details Defined in System.Timeout Methods showsPrec :: Int -> Timeout -> ShowS # show :: Timeout -> String # showList :: [Timeout] -> ShowS #
Show FormatMode |
Instance details Defined in Data.ByteString.Builder.RealFloat Methods showsPrec :: Int -> FormatMode -> ShowS # show :: FormatMode -> String # showList :: [FormatMode] -> ShowS #
Show ByteString |
Instance details Defined in Data.ByteString.Internal.Type Methods showsPrec :: Int -> ByteString -> ShowS # show :: ByteString -> String # showList :: [ByteString] -> ShowS #
Show SizeOverflowException |
Instance details Defined in Data.ByteString.Internal.Type Methods showsPrec :: Int -> SizeOverflowException -> ShowS # show :: SizeOverflowException -> String # showList :: [SizeOverflowException] -> ShowS #
Show ByteString |
Instance details Defined in Data.ByteString.Lazy.Internal Methods showsPrec :: Int -> ByteString -> ShowS # show :: ByteString -> String # showList :: [ByteString] -> ShowS #
Show ShortByteString |
Instance details Defined in Data.ByteString.Short.Internal Methods showsPrec :: Int -> ShortByteString -> ShowS # show :: ShortByteString -> String # showList :: [ShortByteString] -> ShowS #
Show IntSet |
Instance details Defined in Data.IntSet.Internal Methods showsPrec :: Int -> IntSet -> ShowS # show :: IntSet -> String # showList :: [IntSet] -> ShowS #
Show BitQueue |
Instance details Defined in Utils.Containers.Internal.BitQueue Methods showsPrec :: Int -> BitQueue -> ShowS # show :: BitQueue -> String # showList :: [BitQueue] -> ShowS #
Show BitQueueB |
Instance details Defined in Utils.Containers.Internal.BitQueue Methods showsPrec :: Int -> BitQueueB -> ShowS # show :: BitQueueB -> String # showList :: [BitQueueB] -> ShowS #
Show Void | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Void -> ShowS # show :: Void -> String # showList :: [Void] -> ShowS #
Show SomeTypeRep | @since base-4.10.0.0
Instance details Defined in GHC.Internal.Data.Typeable.Internal Methods showsPrec :: Int -> SomeTypeRep -> ShowS # show :: SomeTypeRep -> String # showList :: [SomeTypeRep] -> ShowS #
Show Version | @since base-2.01
Instance details Defined in GHC.Internal.Data.Version Methods showsPrec :: Int -> Version -> ShowS # show :: Version -> String # showList :: [Version] -> ShowS #
Show ArithException | @since base-4.0.0.0
Instance details Defined in GHC.Internal.Exception.Type Methods showsPrec :: Int -> ArithException -> ShowS # show :: ArithException -> String # showList :: [ArithException] -> ShowS #
Show SomeException | Since: ghc-internal-3.0
Instance details Defined in GHC.Internal.Exception.Type Methods showsPrec :: Int -> SomeException -> ShowS # show :: SomeException -> String # showList :: [SomeException] -> ShowS #
Show CBool |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CBool -> ShowS # show :: CBool -> String # showList :: [CBool] -> ShowS #
Show CChar |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CChar -> ShowS # show :: CChar -> String # showList :: [CChar] -> ShowS #
Show CClock |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CClock -> ShowS # show :: CClock -> String # showList :: [CClock] -> ShowS #
Show CDouble |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CDouble -> ShowS # show :: CDouble -> String # showList :: [CDouble] -> ShowS #
Show CFloat |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CFloat -> ShowS # show :: CFloat -> String # showList :: [CFloat] -> ShowS #
Show CInt |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CInt -> ShowS # show :: CInt -> String # showList :: [CInt] -> ShowS #
Show CIntMax |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CIntMax -> ShowS # show :: CIntMax -> String # showList :: [CIntMax] -> ShowS #
Show CIntPtr |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CIntPtr -> ShowS # show :: CIntPtr -> String # showList :: [CIntPtr] -> ShowS #
Show CLLong |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CLLong -> ShowS # show :: CLLong -> String # showList :: [CLLong] -> ShowS #
Show CLong |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CLong -> ShowS # show :: CLong -> String # showList :: [CLong] -> ShowS #
Show CPtrdiff |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CPtrdiff -> ShowS # show :: CPtrdiff -> String # showList :: [CPtrdiff] -> ShowS #
Show CSChar |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CSChar -> ShowS # show :: CSChar -> String # showList :: [CSChar] -> ShowS #
Show CSUSeconds |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CSUSeconds -> ShowS # show :: CSUSeconds -> String # showList :: [CSUSeconds] -> ShowS #
Show CShort |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CShort -> ShowS # show :: CShort -> String # showList :: [CShort] -> ShowS #
Show CSigAtomic |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CSigAtomic -> ShowS # show :: CSigAtomic -> String # showList :: [CSigAtomic] -> ShowS #
Show CSize |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CSize -> ShowS # show :: CSize -> String # showList :: [CSize] -> ShowS #
Show CTime |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CTime -> ShowS # show :: CTime -> String # showList :: [CTime] -> ShowS #
Show CUChar |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CUChar -> ShowS # show :: CUChar -> String # showList :: [CUChar] -> ShowS #
Show CUInt |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CUInt -> ShowS # show :: CUInt -> String # showList :: [CUInt] -> ShowS #
Show CUIntMax |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CUIntMax -> ShowS # show :: CUIntMax -> String # showList :: [CUIntMax] -> ShowS #
Show CUIntPtr |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CUIntPtr -> ShowS # show :: CUIntPtr -> String # showList :: [CUIntPtr] -> ShowS #
Show CULLong |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CULLong -> ShowS # show :: CULLong -> String # showList :: [CULLong] -> ShowS #
Show CULong |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CULong -> ShowS # show :: CULong -> String # showList :: [CULong] -> ShowS #
Show CUSeconds |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CUSeconds -> ShowS # show :: CUSeconds -> String # showList :: [CUSeconds] -> ShowS #
Show CUShort |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CUShort -> ShowS # show :: CUShort -> String # showList :: [CUShort] -> ShowS #
Show CWchar |
Instance details Defined in GHC.Internal.Foreign.C.Types Methods showsPrec :: Int -> CWchar -> ShowS # show :: CWchar -> String # showList :: [CWchar] -> ShowS #
Show Associativity | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> Associativity -> ShowS # show :: Associativity -> String # showList :: [Associativity] -> ShowS #
Show DecidedStrictness | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> DecidedStrictness -> ShowS # show :: DecidedStrictness -> String # showList :: [DecidedStrictness] -> ShowS #
Show Fixity | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> Fixity -> ShowS # show :: Fixity -> String # showList :: [Fixity] -> ShowS #
Show SourceStrictness | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> SourceStrictness -> ShowS # show :: SourceStrictness -> String # showList :: [SourceStrictness] -> ShowS #
Show SourceUnpackedness | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> SourceUnpackedness -> ShowS # show :: SourceUnpackedness -> String # showList :: [SourceUnpackedness] -> ShowS #
Show MaskingState | @since base-4.3.0.0
Instance details Defined in GHC.Internal.IO Methods showsPrec :: Int -> MaskingState -> ShowS # show :: MaskingState -> String # showList :: [MaskingState] -> ShowS #
Show AllocationLimitExceeded | @since base-4.7.1.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> AllocationLimitExceeded -> ShowS # show :: AllocationLimitExceeded -> String # showList :: [AllocationLimitExceeded] -> ShowS #
Show ArrayException | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> ArrayException -> ShowS # show :: ArrayException -> String # showList :: [ArrayException] -> ShowS #
Show AssertionFailed | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> AssertionFailed -> ShowS # show :: AssertionFailed -> String # showList :: [AssertionFailed] -> ShowS #
Show AsyncException | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> AsyncException -> ShowS # show :: AsyncException -> String # showList :: [AsyncException] -> ShowS #
Show BlockedIndefinitelyOnMVar | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> BlockedIndefinitelyOnMVar -> ShowS # show :: BlockedIndefinitelyOnMVar -> String # showList :: [BlockedIndefinitelyOnMVar] -> ShowS #
Show BlockedIndefinitelyOnSTM | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> BlockedIndefinitelyOnSTM -> ShowS # show :: BlockedIndefinitelyOnSTM -> String # showList :: [BlockedIndefinitelyOnSTM] -> ShowS #
Show CompactionFailed | @since base-4.10.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> CompactionFailed -> ShowS # show :: CompactionFailed -> String # showList :: [CompactionFailed] -> ShowS #
Show Deadlock | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> Deadlock -> ShowS # show :: Deadlock -> String # showList :: [Deadlock] -> ShowS #
Show ExitCode |
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> ExitCode -> ShowS # show :: ExitCode -> String # showList :: [ExitCode] -> ShowS #
Show FixIOException | @since base-4.11.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> FixIOException -> ShowS # show :: FixIOException -> String # showList :: [FixIOException] -> ShowS #
Show IOErrorType | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> IOErrorType -> ShowS # show :: IOErrorType -> String # showList :: [IOErrorType] -> ShowS #
Show IOException | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> IOException -> ShowS # show :: IOException -> String # showList :: [IOException] -> ShowS #
Show SomeAsyncException | @since base-4.7.0.0
Instance details Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> SomeAsyncException -> ShowS # show :: SomeAsyncException -> String # showList :: [SomeAsyncException] -> ShowS #
Show BufferMode | @since base-4.2.0.0
Instance details Defined in GHC.Internal.IO.Handle.Types Methods showsPrec :: Int -> BufferMode -> ShowS # show :: BufferMode -> String # showList :: [BufferMode] -> ShowS #
Show Handle | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Handle.Types Methods showsPrec :: Int -> Handle -> ShowS # show :: Handle -> String # showList :: [Handle] -> ShowS #
Show HandleType | @since base-4.1.0.0
Instance details Defined in GHC.Internal.IO.Handle.Types Methods showsPrec :: Int -> HandleType -> ShowS # show :: HandleType -> String # showList :: [HandleType] -> ShowS #
Show Newline | @since base-4.3.0.0
Instance details Defined in GHC.Internal.IO.Handle.Types Methods showsPrec :: Int -> Newline -> ShowS # show :: Newline -> String # showList :: [Newline] -> ShowS #
Show NewlineMode | @since base-4.3.0.0
Instance details Defined in GHC.Internal.IO.Handle.Types Methods showsPrec :: Int -> NewlineMode -> ShowS # show :: NewlineMode -> String # showList :: [NewlineMode] -> ShowS #
Show Int16 | @since base-2.01
Instance details Defined in GHC.Internal.Int Methods showsPrec :: Int -> Int16 -> ShowS # show :: Int16 -> String # showList :: [Int16] -> ShowS #
Show Int32 | @since base-2.01
Instance details Defined in GHC.Internal.Int Methods showsPrec :: Int -> Int32 -> ShowS # show :: Int32 -> String # showList :: [Int32] -> ShowS #
Show Int64 | @since base-2.01
Instance details Defined in GHC.Internal.Int Methods showsPrec :: Int -> Int64 -> ShowS # show :: Int64 -> String # showList :: [Int64] -> ShowS #
Show Int8 | @since base-2.01
Instance details Defined in GHC.Internal.Int Methods showsPrec :: Int -> Int8 -> ShowS # show :: Int8 -> String # showList :: [Int8] -> ShowS #
Show FractionalExponentBase |
Instance details Defined in GHC.Internal.Real Methods showsPrec :: Int -> FractionalExponentBase -> ShowS # show :: FractionalExponentBase -> String # showList :: [FractionalExponentBase] -> ShowS #
Show CallStack | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> CallStack -> ShowS # show :: CallStack -> String # showList :: [CallStack] -> ShowS #
Show SrcLoc | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> SrcLoc -> ShowS # show :: SrcLoc -> String # showList :: [SrcLoc] -> ShowS #
Show Word16 | @since base-2.01
Instance details Defined in GHC.Internal.Word Methods showsPrec :: Int -> Word16 -> ShowS # show :: Word16 -> String # showList :: [Word16] -> ShowS #
Show Word32 | @since base-2.01
Instance details Defined in GHC.Internal.Word Methods showsPrec :: Int -> Word32 -> ShowS # show :: Word32 -> String # showList :: [Word32] -> ShowS #
Show Word64 | @since base-2.01
Instance details Defined in GHC.Internal.Word Methods showsPrec :: Int -> Word64 -> ShowS # show :: Word64 -> String # showList :: [Word64] -> ShowS #
Show Word8 | @since base-2.01
Instance details Defined in GHC.Internal.Word Methods showsPrec :: Int -> Word8 -> ShowS # show :: Word8 -> String # showList :: [Word8] -> ShowS #
Show KindRep |
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> KindRep -> ShowS # show :: KindRep -> String # showList :: [KindRep] -> ShowS #
Show Module | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Module -> ShowS # show :: Module -> String # showList :: [Module] -> ShowS #
Show Ordering | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Ordering -> ShowS # show :: Ordering -> String # showList :: [Ordering] -> ShowS #
Show TrName | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> TrName -> ShowS # show :: TrName -> String # showList :: [TrName] -> ShowS #
Show TyCon | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> TyCon -> ShowS # show :: TyCon -> String # showList :: [TyCon] -> ShowS #
Show TypeLitSort | @since base-4.11.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> TypeLitSort -> ShowS # show :: TypeLitSort -> String # showList :: [TypeLitSort] -> ShowS #
Show OsChar |
Instance details Defined in System.OsString.Internal.Types Methods showsPrec :: Int -> OsChar -> ShowS # show :: OsChar -> String # showList :: [OsChar] -> ShowS #
Show OsString | On windows, decodes as UCS-2. On unix prints the raw bytes without decoding.
Instance details Defined in System.OsString.Internal.Types Methods showsPrec :: Int -> OsString -> ShowS # show :: OsString -> String # showList :: [OsString] -> ShowS #
Show PosixChar |
Instance details Defined in System.OsString.Internal.Types Methods showsPrec :: Int -> PosixChar -> ShowS # show :: PosixChar -> String # showList :: [PosixChar] -> ShowS #
Show PosixString | Prints the raw bytes without decoding.
Instance details Defined in System.OsString.Internal.Types Methods showsPrec :: Int -> PosixString -> ShowS # show :: PosixString -> String # showList :: [PosixString] -> ShowS #
Show WindowsChar |
Instance details Defined in System.OsString.Internal.Types Methods showsPrec :: Int -> WindowsChar -> ShowS # show :: WindowsChar -> String # showList :: [WindowsChar] -> ShowS #
Show WindowsString | Decodes as UCS-2.
Instance details Defined in System.OsString.Internal.Types Methods showsPrec :: Int -> WindowsString -> ShowS # show :: WindowsString -> String # showList :: [WindowsString] -> ShowS #
Show Mode |
Instance details Defined in Text.PrettyPrint.Annotated.HughesPJ Methods showsPrec :: Int -> Mode -> ShowS # show :: Mode -> String # showList :: [Mode] -> ShowS #
Show Style |
Instance details Defined in Text.PrettyPrint.Annotated.HughesPJ Methods showsPrec :: Int -> Style -> ShowS # show :: Style -> String # showList :: [Style] -> ShowS #
Show TextDetails |
Instance details Defined in Text.PrettyPrint.Annotated.HughesPJ Methods showsPrec :: Int -> TextDetails -> ShowS # show :: TextDetails -> String # showList :: [TextDetails] -> ShowS #
Show Doc |
Instance details Defined in Text.PrettyPrint.HughesPJ Methods showsPrec :: Int -> Doc -> ShowS # show :: Doc -> String # showList :: [Doc] -> ShowS #
Show Decoding |
Instance details Defined in Data.Text.Encoding Methods showsPrec :: Int -> Decoding -> ShowS # show :: Decoding -> String # showList :: [Decoding] -> ShowS #
Show UnicodeException |
Instance details Defined in Data.Text.Encoding.Error Methods showsPrec :: Int -> UnicodeException -> ShowS # show :: UnicodeException -> String # showList :: [UnicodeException] -> ShowS #
Show I8 |
Instance details Defined in Data.Text.Foreign Methods showsPrec :: Int -> I8 -> ShowS # show :: I8 -> String # showList :: [I8] -> ShowS #
Show Builder |
Instance details Defined in Data.Text.Internal.Builder Methods showsPrec :: Int -> Builder -> ShowS # show :: Builder -> String # showList :: [Builder] -> ShowS #
Show PartialUtf8CodePoint |
Instance details Defined in Data.Text.Internal.Encoding Methods showsPrec :: Int -> PartialUtf8CodePoint -> ShowS # show :: PartialUtf8CodePoint -> String # showList :: [PartialUtf8CodePoint] -> ShowS #
Show Utf8State |
Instance details Defined in Data.Text.Internal.Encoding Methods showsPrec :: Int -> Utf8State -> ShowS # show :: Utf8State -> String # showList :: [Utf8State] -> ShowS #
Show DecoderState |
Instance details Defined in Data.Text.Internal.Encoding.Utf8 Methods showsPrec :: Int -> DecoderState -> ShowS # show :: DecoderState -> String # showList :: [DecoderState] -> ShowS #
Show Size |
Instance details Defined in Data.Text.Internal.Fusion.Size Methods showsPrec :: Int -> Size -> ShowS # show :: Size -> String # showList :: [Size] -> ShowS #
Show FPFormat |
Instance details Defined in Data.Text.Lazy.Builder.RealFloat Methods showsPrec :: Int -> FPFormat -> ShowS # show :: FPFormat -> String # showList :: [FPFormat] -> ShowS #
Show Iter |
Instance details Defined in Data.Text.Unsafe Methods showsPrec :: Int -> Iter -> ShowS # show :: Iter -> String # showList :: [Iter] -> ShowS #
Show SubHashPath |
Instance details Defined in Data.HashMap.Internal.Debug Methods showsPrec :: Int -> SubHashPath -> ShowS # show :: SubHashPath -> String # showList :: [SubHashPath] -> ShowS #
Show Size |
Instance details Defined in Data.Vector.Fusion.Bundle.Size Methods showsPrec :: Int -> Size -> ShowS # show :: Size -> String # showList :: [Size] -> ShowS #
Show Integer | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Integer -> ShowS # show :: Integer -> String # showList :: [Integer] -> ShowS #
Show Natural | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Natural -> ShowS # show :: Natural -> String # showList :: [Natural] -> ShowS #
Show () | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> () -> ShowS # show :: () -> String # showList :: [()] -> ShowS #
Show Bool | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Bool -> ShowS # show :: Bool -> String # showList :: [Bool] -> ShowS #
Show Char | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Char -> ShowS # show :: Char -> String # showList :: [Char] -> ShowS #
Show Int | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Int -> ShowS # show :: Int -> String # showList :: [Int] -> ShowS #
Show Levity | @since base-4.15.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Levity -> ShowS # show :: Levity -> String # showList :: [Levity] -> ShowS #
Show RuntimeRep | @since base-4.11.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> RuntimeRep -> ShowS # show :: RuntimeRep -> String # showList :: [RuntimeRep] -> ShowS #
Show VecCount | @since base-4.11.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> VecCount -> ShowS # show :: VecCount -> String # showList :: [VecCount] -> ShowS #
Show VecElem | @since base-4.11.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> VecElem -> ShowS # show :: VecElem -> String # showList :: [VecElem] -> ShowS #
Show Word | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Word -> ShowS # show :: Word -> String # showList :: [Word] -> ShowS #
Show a => Show (Complex a) | Since: base-2.1
Instance details Defined in Data.Complex Methods showsPrec :: Int -> Complex a -> ShowS # show :: Complex a -> String # showList :: [Complex a] -> ShowS #
Show a => Show (First a) | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods showsPrec :: Int -> First a -> ShowS # show :: First a -> String # showList :: [First a] -> ShowS #
Show a => Show (Last a) | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods showsPrec :: Int -> Last a -> ShowS # show :: Last a -> String # showList :: [Last a] -> ShowS #
Show a => Show (Max a) | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods showsPrec :: Int -> Max a -> ShowS # show :: Max a -> String # showList :: [Max a] -> ShowS #
Show a => Show (Min a) | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods showsPrec :: Int -> Min a -> ShowS # show :: Min a -> String # showList :: [Min a] -> ShowS #
Show m => Show (WrappedMonoid m) | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods showsPrec :: Int -> WrappedMonoid m -> ShowS # show :: WrappedMonoid m -> String # showList :: [WrappedMonoid m] -> ShowS #
Show vertex => Show (SCC vertex) | Since: containers-0.5.9
Instance details Defined in Data.Graph Methods showsPrec :: Int -> SCC vertex -> ShowS # show :: SCC vertex -> String # showList :: [SCC vertex] -> ShowS #
Show a => Show (IntMap a) |
Instance details Defined in Data.IntMap.Internal Methods showsPrec :: Int -> IntMap a -> ShowS # show :: IntMap a -> String # showList :: [IntMap a] -> ShowS #
Show a => Show (Seq a) |
Instance details Defined in Data.Sequence.Internal Methods showsPrec :: Int -> Seq a -> ShowS # show :: Seq a -> String # showList :: [Seq a] -> ShowS #
Show a => Show (ViewL a) |
Instance details Defined in Data.Sequence.Internal Methods showsPrec :: Int -> ViewL a -> ShowS # show :: ViewL a -> String # showList :: [ViewL a] -> ShowS #
Show a => Show (ViewR a) |
Instance details Defined in Data.Sequence.Internal Methods showsPrec :: Int -> ViewR a -> ShowS # show :: ViewR a -> String # showList :: [ViewR a] -> ShowS #
Show a => Show (Intersection a) |
Instance details Defined in Data.Set.Internal Methods showsPrec :: Int -> Intersection a -> ShowS # show :: Intersection a -> String # showList :: [Intersection a] -> ShowS #
Show a => Show (Set a) |
Instance details Defined in Data.Set.Internal Methods showsPrec :: Int -> Set a -> ShowS # show :: Set a -> String # showList :: [Set a] -> ShowS #
Show a => Show (Tree a) |
Instance details Defined in Data.Tree Methods showsPrec :: Int -> Tree a -> ShowS # show :: Tree a -> String # showList :: [Tree a] -> ShowS #
Show a => Show (NonEmpty a) | @since base-4.11.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> NonEmpty a -> ShowS # show :: NonEmpty a -> String # showList :: [NonEmpty a] -> ShowS #
Show a => Show (Down a) | This instance would be equivalent to the derived instances of the `Down` newtype if the `getDown` field were removed @since base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Ord Methods showsPrec :: Int -> Down a -> ShowS # show :: Down a -> String # showList :: [Down a] -> ShowS #
Show a => Show (ExceptionWithContext a) |
Instance details Defined in GHC.Internal.Exception.Type Methods showsPrec :: Int -> ExceptionWithContext a -> ShowS # show :: ExceptionWithContext a -> String # showList :: [ExceptionWithContext a] -> ShowS #
Show e => Show (NoBacktrace e) |
Instance details Defined in GHC.Internal.Exception.Type Methods showsPrec :: Int -> NoBacktrace e -> ShowS # show :: NoBacktrace e -> String # showList :: [NoBacktrace e] -> ShowS #
Show p => Show (Par1 p) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> Par1 p -> ShowS # show :: Par1 p -> String # showList :: [Par1 p] -> ShowS #
Show a => Show (Ratio a) | @since base-2.0.1
Instance details Defined in GHC.Internal.Real Methods showsPrec :: Int -> Ratio a -> ShowS # show :: Ratio a -> String # showList :: [Ratio a] -> ShowS #
Show a => Show (Hashed a) |
Instance details Defined in Data.Hashable.Class Methods showsPrec :: Int -> Hashed a -> ShowS # show :: Hashed a -> String # showList :: [Hashed a] -> ShowS #
Show a => Show (AnnotDetails a) |
Instance details Defined in Text.PrettyPrint.Annotated.HughesPJ Methods showsPrec :: Int -> AnnotDetails a -> ShowS # show :: AnnotDetails a -> String # showList :: [AnnotDetails a] -> ShowS #
Show (Doc a) |
Instance details Defined in Text.PrettyPrint.Annotated.HughesPJ Methods showsPrec :: Int -> Doc a -> ShowS # show :: Doc a -> String # showList :: [Doc a] -> ShowS #
Show a => Show (Span a) |
Instance details Defined in Text.PrettyPrint.Annotated.HughesPJ Methods showsPrec :: Int -> Span a -> ShowS # show :: Span a -> String # showList :: [Span a] -> ShowS #
Show a => Show (Array a) |
Instance details Defined in Data.Primitive.Array Methods showsPrec :: Int -> Array a -> ShowS # show :: Array a -> String # showList :: [Array a] -> ShowS #
(Show a, Prim a) => Show (PrimArray a) | Since: primitive-0.6.4.0
Instance details Defined in Data.Primitive.PrimArray Methods showsPrec :: Int -> PrimArray a -> ShowS # show :: PrimArray a -> String # showList :: [PrimArray a] -> ShowS #
Show a => Show (SmallArray a) |
Instance details Defined in Data.Primitive.SmallArray Methods showsPrec :: Int -> SmallArray a -> ShowS # show :: SmallArray a -> String # showList :: [SmallArray a] -> ShowS #
Show a => Show (Array a) |
Instance details Defined in Data.HashMap.Internal.Array Methods showsPrec :: Int -> Array a -> ShowS # show :: Array a -> String # showList :: [Array a] -> ShowS #
Show k => Show (Error k) |
Instance details Defined in Data.HashMap.Internal.Debug Methods showsPrec :: Int -> Error k -> ShowS # show :: Error k -> String # showList :: [Error k] -> ShowS #
Show k => Show (Validity k) |
Instance details Defined in Data.HashMap.Internal.Debug Methods showsPrec :: Int -> Validity k -> ShowS # show :: Validity k -> String # showList :: [Validity k] -> ShowS #
Show a => Show (HashSet a) |
Instance details Defined in Data.HashSet.Internal Methods showsPrec :: Int -> HashSet a -> ShowS # show :: HashSet a -> String # showList :: [HashSet a] -> ShowS #
Show a => Show (Vector a) |
Instance details Defined in Data.Vector Methods showsPrec :: Int -> Vector a -> ShowS # show :: Vector a -> String # showList :: [Vector a] -> ShowS #
(Show a, Prim a) => Show (Vector a) |
Instance details Defined in Data.Vector.Primitive Methods showsPrec :: Int -> Vector a -> ShowS # show :: Vector a -> String # showList :: [Vector a] -> ShowS #
(Show a, Storable a) => Show (Vector a) |
Instance details Defined in Data.Vector.Storable Methods showsPrec :: Int -> Vector a -> ShowS # show :: Vector a -> String # showList :: [Vector a] -> ShowS #
Show a => Show (Vector a) |
Instance details Defined in Data.Vector.Strict Methods showsPrec :: Int -> Vector a -> ShowS # show :: Vector a -> String # showList :: [Vector a] -> ShowS #
Show a => Show (Maybe a) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Maybe a -> ShowS # show :: Maybe a -> String # showList :: [Maybe a] -> ShowS #
Show a => Show (Solo a) | @since base-4.15
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Solo a -> ShowS # show :: Solo a -> String # showList :: [Solo a] -> ShowS #
Show a => Show [a] | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> [a] -> ShowS # show :: [a] -> String # showList :: [[a]] -> ShowS #
HasResolution a => Show (Fixed a) | Since: base-2.1
Instance details Defined in Data.Fixed Methods showsPrec :: Int -> Fixed a -> ShowS # show :: Fixed a -> String # showList :: [Fixed a] -> ShowS #
(Show a, Show b) => Show (Arg a b) | Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods showsPrec :: Int -> Arg a b -> ShowS # show :: Arg a b -> String # showList :: [Arg a b] -> ShowS #
(Show k, Show a) => Show (Map k a) |
Instance details Defined in Data.Map.Internal Methods showsPrec :: Int -> Map k a -> ShowS # show :: Map k a -> String # showList :: [Map k a] -> ShowS #
(Show a, Show b) => Show (Either a b) | @since base-3.0
Instance details Defined in GHC.Internal.Data.Either Methods showsPrec :: Int -> Either a b -> ShowS # show :: Either a b -> String # showList :: [Either a b] -> ShowS #
Show (TypeRep a) |
Instance details Defined in GHC.Internal.Data.Typeable.Internal Methods showsPrec :: Int -> TypeRep a -> ShowS # show :: TypeRep a -> String # showList :: [TypeRep a] -> ShowS #
Show (U1 p) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> U1 p -> ShowS # show :: U1 p -> String # showList :: [U1 p] -> ShowS #
Show (V1 p) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> V1 p -> ShowS # show :: V1 p -> String # showList :: [V1 p] -> ShowS #
(Show1 f, Show a) => Show (Lift f a) |
Instance details Defined in Control.Applicative.Lift Methods showsPrec :: Int -> Lift f a -> ShowS # show :: Lift f a -> String # showList :: [Lift f a] -> ShowS #
(Show1 m, Show a) => Show (MaybeT m a) |
Instance details Defined in Control.Monad.Trans.Maybe Methods showsPrec :: Int -> MaybeT m a -> ShowS # show :: MaybeT m a -> String # showList :: [MaybeT m a] -> ShowS #
(Show k, Show v) => Show (HashMap k v) |
Instance details Defined in Data.HashMap.Internal Methods showsPrec :: Int -> HashMap k v -> ShowS # show :: HashMap k v -> String # showList :: [HashMap k v] -> ShowS #
(Show a, Show b) => Show (a, b) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b) -> ShowS # show :: (a, b) -> String # showList :: [(a, b)] -> ShowS #
Show (f p) => Show (Rec1 f p) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> Rec1 f p -> ShowS # show :: Rec1 f p -> String # showList :: [Rec1 f p] -> ShowS #
Show (URec Char p) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> URec Char p -> ShowS # show :: URec Char p -> String # showList :: [URec Char p] -> ShowS #
Show (URec Double p) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> URec Double p -> ShowS # show :: URec Double p -> String # showList :: [URec Double p] -> ShowS #
Show (URec Float p) |
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> URec Float p -> ShowS # show :: URec Float p -> String # showList :: [URec Float p] -> ShowS #
Show (URec Int p) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> URec Int p -> ShowS # show :: URec Int p -> String # showList :: [URec Int p] -> ShowS #
Show (URec Word p) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> URec Word p -> ShowS # show :: URec Word p -> String # showList :: [URec Word p] -> ShowS #
(Show1 f, Show a) => Show (Backwards f a) |
Instance details Defined in Control.Applicative.Backwards Methods showsPrec :: Int -> Backwards f a -> ShowS # show :: Backwards f a -> String # showList :: [Backwards f a] -> ShowS #
(Show e, Show1 m, Show a) => Show (ExceptT e m a) |
Instance details Defined in Control.Monad.Trans.Except Methods showsPrec :: Int -> ExceptT e m a -> ShowS # show :: ExceptT e m a -> String # showList :: [ExceptT e m a] -> ShowS #
(Show1 f, Show a) => Show (IdentityT f a) |
Instance details Defined in Control.Monad.Trans.Identity Methods showsPrec :: Int -> IdentityT f a -> ShowS # show :: IdentityT f a -> String # showList :: [IdentityT f a] -> ShowS #
(Show w, Show1 m, Show a) => Show (WriterT w m a) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods showsPrec :: Int -> WriterT w m a -> ShowS # show :: WriterT w m a -> String # showList :: [WriterT w m a] -> ShowS #
(Show w, Show1 m, Show a) => Show (WriterT w m a) |
Instance details Defined in Control.Monad.Trans.Writer.Strict Methods showsPrec :: Int -> WriterT w m a -> ShowS # show :: WriterT w m a -> String # showList :: [WriterT w m a] -> ShowS #
Show a => Show (Constant a b) |
Instance details Defined in Data.Functor.Constant Methods showsPrec :: Int -> Constant a b -> ShowS # show :: Constant a b -> String # showList :: [Constant a b] -> ShowS #
(Show1 f, Show a) => Show (Reverse f a) |
Instance details Defined in Data.Functor.Reverse Methods showsPrec :: Int -> Reverse f a -> ShowS # show :: Reverse f a -> String # showList :: [Reverse f a] -> ShowS #
(Show a, Show b, Show c) => Show (a, b, c) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c) -> ShowS # show :: (a, b, c) -> String # showList :: [(a, b, c)] -> ShowS #
(Show (f a), Show (g a)) => Show (Product f g a) | Since: base-4.18.0.0
Instance details Defined in Data.Functor.Product Methods showsPrec :: Int -> Product f g a -> ShowS # show :: Product f g a -> String # showList :: [Product f g a] -> ShowS #
(Show (f a), Show (g a)) => Show (Sum f g a) | Since: base-4.18.0.0
Instance details Defined in Data.Functor.Sum Methods showsPrec :: Int -> Sum f g a -> ShowS # show :: Sum f g a -> String # showList :: [Sum f g a] -> ShowS #
(Show (f p), Show (g p)) => Show ((f :*: g) p) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> (f :*: g) p -> ShowS # show :: (f :*: g) p -> String # showList :: [(f :*: g) p] -> ShowS #
(Show (f p), Show (g p)) => Show ((f :+: g) p) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> (f :+: g) p -> ShowS # show :: (f :+: g) p -> String # showList :: [(f :+: g) p] -> ShowS #
Show c => Show (K1 i c p) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> K1 i c p -> ShowS # show :: K1 i c p -> String # showList :: [K1 i c p] -> ShowS #
(Show a, Show b, Show c, Show d) => Show (a, b, c, d) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d) -> ShowS # show :: (a, b, c, d) -> String # showList :: [(a, b, c, d)] -> ShowS #
Show (f (g a)) => Show (Compose f g a) | Since: base-4.18.0.0
Instance details Defined in Data.Functor.Compose Methods showsPrec :: Int -> Compose f g a -> ShowS # show :: Compose f g a -> String # showList :: [Compose f g a] -> ShowS #
Show (f (g p)) => Show ((f :.: g) p) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> (f :.: g) p -> ShowS # show :: (f :.: g) p -> String # showList :: [(f :.: g) p] -> ShowS #
Show (f p) => Show (M1 i c f p) | @since base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods showsPrec :: Int -> M1 i c f p -> ShowS # show :: M1 i c f p -> String # showList :: [M1 i c f p] -> ShowS #
(Show a, Show b, Show c, Show d, Show e) => Show (a, b, c, d, e) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e) -> ShowS # show :: (a, b, c, d, e) -> String # showList :: [(a, b, c, d, e)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f) => Show (a, b, c, d, e, f) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f) -> ShowS # show :: (a, b, c, d, e, f) -> String # showList :: [(a, b, c, d, e, f)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f, Show g) => Show (a, b, c, d, e, f, g) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f, g) -> ShowS # show :: (a, b, c, d, e, f, g) -> String # showList :: [(a, b, c, d, e, f, g)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h) => Show (a, b, c, d, e, f, g, h) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f, g, h) -> ShowS # show :: (a, b, c, d, e, f, g, h) -> String # showList :: [(a, b, c, d, e, f, g, h)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i) => Show (a, b, c, d, e, f, g, h, i) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f, g, h, i) -> ShowS # show :: (a, b, c, d, e, f, g, h, i) -> String # showList :: [(a, b, c, d, e, f, g, h, i)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j) => Show (a, b, c, d, e, f, g, h, i, j) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f, g, h, i, j) -> ShowS # show :: (a, b, c, d, e, f, g, h, i, j) -> String # showList :: [(a, b, c, d, e, f, g, h, i, j)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k) => Show (a, b, c, d, e, f, g, h, i, j, k) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f, g, h, i, j, k) -> ShowS # show :: (a, b, c, d, e, f, g, h, i, j, k) -> String # showList :: [(a, b, c, d, e, f, g, h, i, j, k)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l) => Show (a, b, c, d, e, f, g, h, i, j, k, l) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f, g, h, i, j, k, l) -> ShowS # show :: (a, b, c, d, e, f, g, h, i, j, k, l) -> String # showList :: [(a, b, c, d, e, f, g, h, i, j, k, l)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l, Show m) => Show (a, b, c, d, e, f, g, h, i, j, k, l, m) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f, g, h, i, j, k, l, m) -> ShowS # show :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> String # showList :: [(a, b, c, d, e, f, g, h, i, j, k, l, m)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l, Show m, Show n) => Show (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> ShowS # show :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> String # showList :: [(a, b, c, d, e, f, g, h, i, j, k, l, m, n)] -> ShowS #
(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l, Show m, Show n, Show o) => Show (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | @since base-2.01
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> ShowS # show :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> String # showList :: [(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)] -> ShowS #

type ShowS = String -> String #

The `shows` functions return a function that prepends the output `String` to an existing `String`. This allows constant-time concatenation of results using function composition.

shows :: Show a => a -> ShowS #

equivalent to `showsPrec` with a precedence of 0.

showChar :: Char -> ShowS #

utility function converting a `Char` to a show function that simply prepends the character unchanged.

showString :: String -> ShowS #

utility function converting a `String` to a show function that simply prepends the string unchanged.

showParen :: Bool -> ShowS -> ShowS #

utility function that surrounds the inner show function with parentheses when the `Bool` parameter is `True`.

type ReadS a = String -> [(a, String)] #

A parser for a type `a`, represented as a function that takes a `String` and returns a list of possible parses as `(a,`String`)` pairs.

Note that this kind of backtracking parser is very inefficient; reading a large structure may be quite slow (cf `ReadP`).

readsPrec #

Arguments

:: Read a |
=> Int | the operator precedence of the enclosing context (a number from `0` to `11`). Function application has precedence `10`.
-> ReadS a |

attempts to parse a value from the front of the string, returning a list of (parsed value, remaining string) pairs. If there is no successful parse, the returned list is empty.

Derived instances of `Read` and `Show` satisfy the following:

- `(x,"")` is an element of `(`readsPrec` d (`showsPrec` d x ""))`.

That is, `readsPrec` parses the string produced by `showsPrec`, and delivers the value that `showsPrec` started with.

readList :: Read a => ReadS [a] #

The method `readList` is provided to allow the programmer to give a specialised way of parsing lists of values. For example, this is used by the predefined `Read` instance of the `Char` type, where values of type `String` are expected to use double quotes, rather than square brackets.

reads :: Read a => ReadS a #

equivalent to `readsPrec` with a precedence of 0.

readParen :: Bool -> ReadS a -> ReadS a #

``readParen` `True` p` parses what `p` parses, but surrounded with parentheses.

``readParen` `False` p` parses what `p` parses, but optionally surrounded with parentheses.

lex :: ReadS String #

The `lex` function reads a single lexeme from the input, discarding initial white space, and returning the characters that constitute the lexeme. If the input string contains only white space, `lex` returns a single successful `lexeme' consisting of the empty string. (Thus ``lex` "" = [("","")]`.) If there is no legal lexeme at the beginning of the input string, `lex` fails (i.e. returns `[]`).

This lexer is not completely faithful to the Haskell lexical syntax in the following respects:

- Qualified names are not handled properly
- Octal and hexadecimal numerics are not recognized as a single token
- Comments are not treated properly

readMay :: Read a => Text -> Maybe a #

## IO operations

getChar :: MonadIO m => m Char #

Since: 0.7.0

putChar :: MonadIO m => Char -> m () #

Since: 0.7.0

readLn :: (MonadIO m, Read a) => m a #

The `readLn` function combines `getLine` and `readIO`.

Since: 0.7.0