Text.ParserCombinators.Poly.State

polyparse-1.12: A variety of alternative parser combinator libraries.

Safe Haskell | Safe
Language | Haskell98

Text.ParserCombinators.Poly.State

Contents

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

Synopsis

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

# The Parser datatype

newtype Parser s t a

This `Parser` datatype is a fairly generic parsing monad with error reporting, and running state. It can be used for arbitrary token types, not just String input. (If you do not require a running state, use module Poly.Plain instead)

Constructors

P (s -> [t] -> Result ([t], s) a) |

Instances

Monad (Parser s t) |
Functor (Parser s t) |
Applicative (Parser s t) |
Alternative (Parser s t) |
PolyParse (Parser s t) |
Commitment (Parser s t) |

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

Functor (Result z) |

runParser :: Parser s t a -> s -> [t] -> (Either String a, s, [t])

Apply a parser to an input token sequence.

## Basic parsers

next :: Parser s t t

Simply return the next token in the input tokenstream.

eof :: Parser s t ()

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

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

Return the next token if it satisfies the given predicate.

onFail :: Parser s t a -> Parser s t a -> Parser s 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.

## State-handling

stUpdate :: (s -> s) -> Parser s t ()

Update the internal state.

stQuery :: (s -> a) -> Parser s t a

Query the internal state.

stGet :: Parser s t s

Deliver the entire internal state.

## Re-parsing

reparse :: [t] -> Parser s 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