[ ghc-Bugs-755726 ] mutiparameter classes problem

Bugs item #755726, was opened at 2003-06-16 23:24
Message generated for change (Tracker Item Submitted) made by Item Submitter
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Category: Compiler (Type checker)
Group: 6.0
Status: Open
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: mutiparameter classes problem

Initial Comment:
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


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