unsafeCoerce# doesn't always fully coerce

{-# OPTIONS_GHC -fglasgow-exts #-}

import GHC.Prim( unsafeCoerce# )

e1 = unsafeCoerce# (+)
e2 = unsafeCoerce# shows

e1 coerces fine, even with the Num constraint, but e2 does not. The error for e2 is

    Ambiguous type variable `a' in the constraint:
      `Show a' arising from use of `shows' at T.lhs:7:20-24
    Probable fix: add a type signature that fixes these type variable(s)

Weirder still, ghci coerces shows fine:

*Main> :t unsafeCoerce# shows
unsafeCoerce# shows :: forall b. b

Trac metadata

Trac field	Value
Version	6.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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