Core lint error in simplifier when compiling Rules1 with -O -dcore-lint
Running make TEST=Rules1 WAY=optasm
results in a core lint error (see attachment) with ghc-8.0.1-rc2.
This is the code:
{-# LANGUAGE TypeFamilies #-}
module Rules1 where
class C a where
data T a
instance (C a, C b) => C (a,b) where
data T (a,b) = TPair (T a) (T b)
mapT :: (C a, C b) => (a -> b) -> T a -> T b
{-# NOINLINE mapT #-} -- Otherwwise we get a warning from the rule
mapT = undefined
zipT :: (C a, C b) => T a -> T b -> T (a,b)
{-# NOINLINE [1] zipT #-}
zipT = undefined
{-# RULES
"zipT/mapT" forall f x y.
zipT (mapT f x) y = mapT (\(x,y) -> (f x, y)) (zipT x y)
#-}
$ ghc-8.0.1 -O Rules1.hs -dcore-lint
This is a regression from 7.10.3, and core lint errors are bad, so setting priority to highest.