mutiparameter classes problem

hello,
i have run into something that looks like a bug in ghc 6.0.
here is an example:

> module A where
> class C a b where f :: a -> b
> g x = fst (f x)

for this program hugs reports that "g" has an ambiguous
type:
  C a (b,c) => a -> b
which seems reasonable.
however ghc does not report an error, and infers the
following type:
  C a (b, ()) => a -> b
(i have changed the formatting for easier comparing).
it seems that somehow the second component of the tuple
became (),
but i don't see why.

bye
iavor

Trac metadata

Trac field	Value
Version	6.0
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	ResolvedFixed
Component	Compiler (Type checker)
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