[Haskell-cafe] stuck with a sample of "programming in haskell"

[Stephen Tetley]

On 19 March 2010 04:35, 国平张 <zhangguoping at gmail.com> wrote:
> Sorry to bother again. I just cannot figure out how it could compile.
> I got compile errors.
> Can someone point out what is right code to use a do notion to make a
> Parser works.

It looks like the p parser may have the wrong indentation - although
this might be due to either your mail client or my client formatting
wrongly:

p :: Parser (Char,Char)
p = do x <- item
      item
      y <- item
      return (x,y)


Try - with white space all aligned to the start character /x/ of the
first statement in the do:

p :: Parser (Char,Char)
p = do x <- item
       item
       y <- item
       return (x,y)

Or with braces and semis:

p :: Parser (Char,Char)
p = do { x <- item
       ; item
       ; y <- item
       ; return (x,y) }

Best wishes

Stephen