Test Trac #8359

1 files changed, 17 insertions, 0 deletions

diff --git a/testsuite/tests/polykinds/T8359.hs b/testsuite/tests/polykinds/T8359.hs
new file mode 100644
index 0000000000..d172270b12
--- /dev/null
+++ b/testsuite/tests/polykinds/T8359.hs
@@ -0,0 +1,17 @@
+{-# LANGUAGE ConstraintKinds, MultiParamTypeClasses #-}
+module T8359 where
+
+class DifferentTypes a b
+
+type DifferentTypes3 a b c = (DifferentTypes a b, DifferentTypes b c, DifferentTypes a c)
+
+class Foo a
+
+class Bar a
+
+-- Buggy instance requires UndecidableInstances to compile
+
+instance (DifferentTypes3 a b c, Bar a, Bar b, Bar c) => Foo (a, b, c)
+
+-- Equivalent instance compiles when manually expanding constraint type
+-- instance (DifferentTypes a b, DifferentTypes b c, DifferentTypes a c, Bar a, Bar b, Bar c) => Foo (a, b, c)