id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
3342	splitTyConApp panic when using view patterns	guest	igloo	"Here is a sample program that makes ghci panic with the following message:

{{{
ghc: panic! (the 'impossible' happened)
  (GHC version 6.10.3 for i386-unknown-linux):
	splitTyConApp t_ag8{tv} [tau]
}}}

The code uses view patterns.

{{{
module Bug where

data F = FT String [F]
data G = GX F F | GY

spec :: F -> G
spec (FT ""X""  [t1, t2]) = GX t1 t2
spec _                  = GY

walk (spec -> GX _ t2) = walk t2
walk t@(FT _ _)        = t
}}}

You can reach me at cklin@cs.pdx.edu"	merge	closed	normal		Compiler	6.10.3	fixed		cklin@…	Unknown/Multiple	Unknown/Multiple		Unknown	typecheck/should_compiler/T3342