id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
1482	unsafeCoerce# doesn't always fully coerce	yeoh@…		"{{{
{-# 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
}}}"	bug	closed	normal		Compiler (Type checker)	6.6.1	invalid	unsafeCoerce#		Linux	x86		Unknown