id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
7384	"Panic ""ctEvTerm"" when using functional dependencies and PolyKinds"	goldfire		"The following code causes a panic:

{{{
{-# LANGUAGE FunctionalDependencies, PolyKinds #-}

class Baz a b | a -> b where
  bar :: a -> ()

instance Baz Bool Bool where
  bar _ = ()

foo = bar False
}}}

The panic reads:

{{{
ghc: panic! (the 'impossible' happened)
  (GHC version 7.7.20121031 for x86_64-apple-darwin):
	ctEvTerm: derived constraint cannot have id
<<details unavailable>>
}}}

The panic does not happen without {{{-XPolyKinds}}}."	bug	closed	normal		Compiler	7.7	fixed	FunctionalDependencies PolyKinds		Unknown/Multiple	Unknown/Multiple	None/Unknown	Unknown	typecheck/should_compile/T7384