polyparse-1.5: A variety of alternative parser combinator libraries.




This module contains the definitions for a generic parser, with running state. These are the parts that are shared between the State and StateLazy variations. Do not import this module directly, but only via T.P.Poly.State or T.P.Poly.StateLazy.


The Parser datatype

newtype Parser s t a Source

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)


P (s -> [t] -> Result ([t], s) a) 


data Result z a Source

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.


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


basic parsers

next :: Parser s t tSource

Simply return the next token in the input tokenstream.

eof :: Parser s t ()Source

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

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

Return the next token if it satisfies the given predicate.

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

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.


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

Update the internal state.

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

Query the internal state.

stGet :: Parser s t sSource

Deliver the entire internal state.


reparse :: [t] -> Parser s t ()Source

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.