Re: [Haskell-cafe] Parser problem continued

15 Mar 2005

...
expr :: Parser Int
expr = do t <- term
          do symbol "+"
             e <- expr
             return e
          return (t + e)
       +++ return t        <-----
't' is not in scope at the arrow.  t only exists inside the
do block, and your code parses like this

( do t <- .... return (t+e) ) +++ ( return t )

perhaps like this:

expr = do t <- term
           (do symbol "+"
               e <- expr
               return (t+e)
           )
           +++
           (return t)

although I think you may also want a 'try' before the first alternative.

Re: [Haskell-cafe] Parser problem continued

robert dockins