[Haskell-cafe] use of the GHC universal quantifier

Galchin, Vasili vigalchin at gmail.com
Wed Jul 9 00:55:35 EDT 2008


     It seems to me by its name that "forall" denotes a logical universal
quantifier. In any case, hsql-1.7/Database/HSQL/Types.hs uses "forall" at
line #134. I got a nasty build so I added {-# LANGUAGE
ExistentialQuantification #-} at the top of the module. Now I get the
following a coupleof lines up:

    Illegal polymorphic or qualified type: forall a.
                                           -> FieldDef
                                           -> FieldDef
                                           -> CString
                                           -> Int
                                           -> IO a
                                           -> IO a
    In the definition of data constructor `Statement'
    In the data type declaration for `Statement'

If seems that GHC doesn't like "a". Why?

Kind regards, Vasili
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