Type families: T2627b

testsuite/tests/ghc-regress/indexed-types/should_fail/T2627b.hs

+{-# LANGUAGE GADTs, TypeFamilies, EmptyDataDecls #-}
+
+module T2627b where
+
+data R a b
+data W a b
+data Z
+
+type family Dual a
+type instance Dual Z = Z
+type instance Dual (R a b) = W a (Dual b)
+type instance Dual (W a b) = R a (Dual b)
+
+data Comm a where
+    Rd :: (a -> Comm b) -> Comm (R a b)
+    Wr :: a  -> Comm b  -> Comm (W a b)
+    Fin :: Int -> Comm Z
+
+conn :: (Dual a ~ b, Dual b ~ a) => Comm a -> Comm b -> (Int, Int)
+conn (Rd k) (Wr a r) = conn undefined undefined

testsuite/tests/ghc-regress/indexed-types/should_fail/T2627b.stderr

+
+T2627b.hs:20:13:
+    Couldn't match expected type `a'
+           against inferred type `Dual (Dual a)'
+    In the pattern: Wr a r
+    In the definition of `conn':
+        conn (Rd k) (Wr a r) = conn undefined undefined

testsuite/tests/ghc-regress/indexed-types/should_fail/all.T

@@ -30,6 +30,7 @@ test('T2334', normal, compile_fail, [''])
 test('T1900', normal, compile_fail, [''])
 test('T2157', normal, compile_fail, [''])
 test('T2203a', normal, compile_fail, [''])
+test('T2627b', normal, compile_fail, [''])
 
 test('GADTwrong1', normal, compile_fail, [''])