[Haskell-beginners] Parsec 3.0 problems

Ian Duncan iand675 at gmail.com
Mon Apr 20 19:26:35 EDT 2009

Hello everyone,
I have the simple applicative parser combinator:

parseLabel = Label <$> (between spaces (char ':') (many1 alphaNum))

This gives me the error:

No instance for (Stream s m Char)
      arising from a use of `spaces' at tree.hs:18:32-37
    Possible fix: add an instance declaration for (Stream s m Char)
    In the first argument of `between', namely `spaces'
    In the second argument of `(<$>)', namely
        `(between spaces (char ':') (many1 alphaNum))'
    In the expression:
          Label <$> (between spaces (char ':') (many1 alphaNum))

When I test this function in ghci, I have no problems, yet whenever I try to
open it in a file it fails. What am I doing wrong?
For those who are curious, Label is a data constructor in the following data

data Loc = Label String
 | Addr Int
deriving Show

Ian Duncan
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