id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
2856	GeneralizedNewtypeDeriving doesn't work with data families	guest	igloo	"Observe:
{{{
{-# LANGUAGE TypeFamilies, GeneralizedNewtypeDeriving #-}
module Bug9 where

class C a where
    data D a

instance C Bool where
    newtype D Bool = DInt Int deriving (Eq, Show, Num)
}}}
The deriving of Num fails, whereas the corresponding standalone newtype works fine.
"	merge	closed	normal		Compiler	6.10.1	fixed		lennart@…	Unknown/Multiple	Unknown/Multiple		Unknown	deriving/should_compile/T2856