id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
7020	Kind variable generalization problem	goldfire		"Consider the following tangle of definitions:

{{{
{-# LANGUAGE KindSignatures, RankNTypes, PolyKinds, GADTs,
             FlexibleContexts, DataKinds, TypeFamilies #-}

import GHC.Exts

data family Sing (a :: k)
class SingKind (Any :: k) => SingI (s :: k) where
  sing :: Sing s
data SingInstance :: k -> * where 
  SingInstance :: SingI a => SingInstance a
class (b ~ Any) => SingKind (b :: k) where
  singInstance :: forall (a :: k). Sing a -> SingInstance a
}}}

When compiling (with 7.5.20120620), I get this error message:

{{{
    Kind mis-match
    The first argument of `SingKind' should have kind `k1',
    but `Any' has kind `k'
    In the class declaration for `SingI'
}}}

I believe that the code should compile, though I'll admit I'm not 100% convinced."	bug	closed	normal		Compiler	7.5	fixed	PolyKinds		Unknown/Multiple	Unknown/Multiple	GHC rejects valid program	Unknown	polykinds/T7020