Re: [Haskell-cafe] Parsing problem

Am Donnerstag, 26. Juni 2008 12:40 schrieb Eric:

Hi all,

I'm using the Parsec library to parse the following grammar

expr = atom+ atom = integer | var | (expr)

The input to the parser is a list of (Token, SourcePos). I have the following code for atom:

atom = try variable <|> try integerr <|> do{sat(== Reserved "("); (e,pos) <- expression; sat(==Reserved ")"); return (e,pos)}

sat p = do (t,pos) <- item if p t then return(t,pos) else pzero

When I run the code on the input "(_ineg_ 0)" the parser fails, but removing

sat(==Reserved ")")

and it succeeds. Can any one see why?

E.

What does the tokeniser return? I would have to see more of the code to diagnose it. Cheers, Daniel