id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
3851	type family does not get expanded in ghc-6.12.1	kosmikus		"The following code (which is a trimmed down version of an application of the multirec library) does not compile on ghc-6.12.1,
but it does with ghc-6.10.4. Why?

{{{
{-# LANGUAGE GADTs, TypeFamilies #-}
type family TF a :: * -> *
type instance TF () = App (Equ ())

data Equ ix ix' where Refl :: Equ ix ix
data App f x = App (f x)

-- does not typecheck in 6.12.1 (but works in 6.10.4)
bar :: TF () () -> ()
bar (App Refl) = ()

-- does typecheck in 6.12.1 and 6.10.4
ar :: App (Equ ()) () -> ()
ar (App Refl) = ()
}}}"	bug	closed	normal	7.0.1	Compiler (Type checker)	6.12.1	fixed		jpm@… stefan@… andres@…	Unknown/Multiple	Unknown/Multiple	GHC rejects valid program		indexed-types/should_compile/T3851