[Haskell-cafe] Parsing problem

[Eric]

Daniel Fischer wrote:
> Am Donnerstag, 26. Juni 2008 12:40 schrieb Eric:
>   
> What does the tokeniser return?
> I would have to see more of the code to diagnose it.
>   
Here is the code for the tokenizer:

type Scanner a = GenParser Char () a

data Token
  =  INum Integer | FNum Double
     | Varid String | Reserved String
  deriving (Show,Eq)

scan :: Scanner a -> Scanner(a, SourcePos)
scan p = do  pos <- getPosition
                    x <- p
                   return(x,pos)

scan_integer, scan_varid, hreserved, htoken :: Scanner 
(Token,SourcePos)            

scan_integer = do  (i,pos) <- scan(integer (makeTokenParser haskellDef))
                             return (INum i, pos)
                  
scan_varid = do  (c,pos) <- scan(hlower)
                          cs <- identifier(makeTokenParser haskellDef)
                         return (Varid (c:cs), pos)

hlower :: Scanner Char             
hlower = lower <|> char '_'

hreserved = do  (cs, pos) <- scan(string "(" <|> string ")")
                         return (Reserved cs,pos)
             
htoken = scan_integer <|> scan_varid <|> hreserved
                  
scanall :: String -> [(Token,SourcePos)]
scanall cs = let result = parse (many htoken) "" cs
                  in case result of
                         Right tkns -> tkns
                         Left err -> error (show err)

E.