id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
5777	core lint error with arrow notation and GADTs	benmos	ross	"The following code panics GHC (with 7.0.3, 7.2 and 7.4.0.20111219):

{{{
{-# LANGUAGE Arrows, GADTs #-}
import Control.Arrow

data Value a where BoolVal :: Value Bool

class ArrowInit f where
    arrif :: f b -> ()

instance ArrowInit Value where
    arrif = proc BoolVal -> returnA -< ()
    -- arrif = arr (\BoolVal -> ())
}}}

I am attaching the -dcore-lint from 7.4.
"	bug	new	normal	7.6.2	Compiler	7.4.2		arrows, GADTs	ross ben@… benjamin.moseley@… abcz2.uprola@…	MacOS X	Unknown/Multiple	Compile-time crash	Unknown