id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
6102	Subclass Specialization in Rewrite Rules	SamAnklesaria	SamAnklesaria	"Rewrite rules can define a specialized version of a method for some specific datatype, but they cannot currently define a specialized version of a method for some specific superclass.

{{{
class ClassOne a where
   classOneOp :: a -> a 

class ClassOne a => ClassTwo a where
   classTwoOp :: a -> a

data ClassInstance = ...

instance ClassOne ClassInstance where
   classOneOp = ...

specialFunc :: ClassInstance -> ClassInstance
specialFunc = ...

{-# RULES
""willcompile""        forall i. classOneOp i = specialFunc
""wontcompile""      forall i. classOneOp i = classTwoOp i
   #-}
}}}

Although we can specialize ''classOneOp'' for ''ClassInstance'', we can't do so for those instances of ''ClassOne'' that are also instances of ''ClassTwo''.
"	feature request	closed	normal		Compiler	7.4.1	invalid			Unknown/Multiple	Unknown/Multiple	None/Unknown	Unknown