polyparse-1.6: A variety of alternative parser combinator libraries.




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) 


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

Apply a parser to an input token sequence.

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.

Re-export all more general combinators