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0 parameter type classes

This seems to be a problem:

Program:

class Tag where
    f :: Char

main = main 


Output:
 
ghc -c -fglasgow-exts bug_ghc.hs

bug_ghc.hs:2:
    The constraint `Tag' does not mention any of the 
universally quantified type variables
        in the type `(Tag) => Char'
    In the class declaration for `Tag'
Trac metadata
Trac field Value
Version 5.0
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution ResolvedFixed
Component Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture
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