signatures are too permissive

ghc should reject the following (accidentally mistyped) signature, unless -XFlexibleContexts is used.

flex :: Int -> Show a => a -> String
flex i a = show a ++ show i

hugs and ghc version below 7 rejected this correctly:

    All of the type variables in the constraint `Show a'
    are already in scope (at least one must be universally quantified here)
        (Use -XFlexibleContexts to lift this restriction)
    In the type signature for `flex':
      flex :: Int -> (Show a) => a -> String

It is not Haskell98 nor Haskell2010 (I believe).

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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