Text.ParserCombinators.Poly.Lex

polyparse-1.13: A variety of alternative parser combinator libraries.

Safe Haskell | Safe-Inferred
Language | Haskell98

Text.ParserCombinators.Poly.Lex

Contents

- The Parser datatype
  - Basic parsers
  - Re-parsing
- Re-export all more general combinators

Description

In a strict language, where creating the entire input list of tokens in one shot may be infeasible, we can use a lazy "callback" kind of architecture instead. The lexer returns a single token at a time, together with a continuation.

This module defines a Parser type (capable of use with the Poly combinators), specialised to the callback-lexer style of input stream.

Synopsis

- data LexReturn t
  - = LexReturn t String (String -> LexReturn t)
  - | LexFinish
- newtype Parser t a = P (LexReturn t -> Result (LexReturn t) a)
- data Result z a
  - = Success z a
  - | Failure z String
  - | Committed (Result z a)
- runParser :: Parser t a -> LexReturn t -> (Either String a, String)
- next :: Parser t t
- eof :: Parser t ()
- satisfy :: (t -> Bool) -> Parser t t
- onFail :: Parser t a -> Parser t a -> Parser t a
- reparse :: [t] -> Parser t ()
- module Text.ParserCombinators.Poly.Base
- module Control.Applicative

# The Parser datatype

data LexReturn t #

In a strict language, where creating the entire input list of tokens in one shot may be infeasible, we can use a lazy "callback" kind of architecture instead. The lexer returns a single token at a time, together with a continuation. The `next` parser is responsible for pulling on the token stream, applying the continuation where necessary.

Constructors

LexReturn t String (String -> LexReturn t) |
LexFinish |

newtype Parser t a #

This `Parser` datatype is a specialised parsing monad with error reporting. This version is specialised to pre-lexed String input, where the lexer has been written to yield a `LexReturn`.

Constructors

P (LexReturn t -> Result (LexReturn t) a) |

#### Instances

Instances details

Alternative (Parser t) # |
Instance details Defined in Text.ParserCombinators.Poly.Lex Methods empty :: Parser t a # (<|>) :: Parser t a -> Parser t a -> Parser t a # some :: Parser t a -> Parser t [a] # many :: Parser t a -> Parser t [a] #
Applicative (Parser t) # |
Instance details Defined in Text.ParserCombinators.Poly.Lex Methods pure :: a -> Parser t a # (<*>) :: Parser t (a -> b) -> Parser t a -> Parser t b # liftA2 :: (a -> b -> c) -> Parser t a -> Parser t b -> Parser t c # (*>) :: Parser t a -> Parser t b -> Parser t b # (<*) :: Parser t a -> Parser t b -> Parser t a #
Functor (Parser t) # |
Instance details Defined in Text.ParserCombinators.Poly.Lex Methods fmap :: (a -> b) -> Parser t a -> Parser t b # (<$) :: a -> Parser t b -> Parser t a #
Monad (Parser t) # |
Instance details Defined in Text.ParserCombinators.Poly.Lex Methods (>>=) :: Parser t a -> (a -> Parser t b) -> Parser t b # (>>) :: Parser t a -> Parser t b -> Parser t b # return :: a -> Parser t a #
MonadFail (Parser t) # |
Instance details Defined in Text.ParserCombinators.Poly.Lex Methods fail :: String -> Parser t a #
Commitment (Parser t) # |
Instance details Defined in Text.ParserCombinators.Poly.Lex Methods commit :: Parser t a -> Parser t a # adjustErr :: Parser t a -> (String -> String) -> Parser t a # oneOf' :: [(String, Parser t a)] -> Parser t a #
PolyParse (Parser t) # |
Instance details Defined in Text.ParserCombinators.Poly.Lex

data Result z a #

A return type like Either, that distinguishes not only between right and wrong answers, but also has commitment, so that a failure cannot be undone. This should only be used for writing very primitive parsers - really it is an internal detail of the library. The z type is the remaining unconsumed input.

Constructors

Success z a |
Failure z String |
Committed (Result z a) |

#### Instances

Instances details

Functor (Result z) # |
Instance details Defined in Text.ParserCombinators.Poly.Result Methods fmap :: (a -> b) -> Result z a -> Result z b # (<$) :: a -> Result z b -> Result z a #

runParser :: Parser t a -> LexReturn t -> (Either String a, String) #

Apply a parser to an input token sequence.

## Basic parsers

next :: Parser t t #

Simply return the next token in the input tokenstream.

eof :: Parser t () #

Succeed if the end of file/input has been reached, fail otherwise.

satisfy :: (t -> Bool) -> Parser t t #

Return the next token if it satisfies the given predicate.

onFail :: Parser t a -> Parser t a -> Parser t a infixl 6 #

`p `onFail` q` means parse p, unless p fails, in which case parse q instead. Can be chained together to give multiple attempts to parse something. (Note that q could itself be a failing parser, e.g. to change the error message from that defined in p to something different.) However, a severe failure in p cannot be ignored.

## Re-parsing

reparse :: [t] -> Parser t () #

Push some tokens back onto the front of the input stream and reparse. This is useful e.g. for recursively expanding macros. When the user-parser recognises a macro use, it can lookup the macro expansion from the parse state, lex it, and then stuff the lexed expansion back down into the parser.

# Re-export all more general combinators

module Text.ParserCombinators.Poly.Base

module Control.Applicative