[Haskell-cafe] Parsing problem

[Daniel Fischer]

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