Test Trac #7280

testsuite/tests/indexed-types/should_compile/T7280.hs

+{-# LANGUAGE Rank2Types, MultiParamTypeClasses, FlexibleContexts,
+   TypeFamilies, ScopedTypeVariables #-}
+
+module T7280 where
+
+type family Mutable (v :: * -> *) :: * -> * -> *
+class MVector (v :: * -> * -> *) a
+class MVector (Mutable v) a => Vector v a where
+   copy :: Monad m => Mutable v s a -> v a -> m ()
+
+data Chunk v s a = Chunk (forall m. (Monad m, Vector v a) => Mutable v s a -> m ())
+
+vstep (v:vs) = Chunk (\mv -> copy mv v)

testsuite/tests/indexed-types/should_compile/all.T

@@ -199,5 +199,6 @@ test('T7082', normal, compile, [''])
 test('T7156', normal, compile, [''])
 test('T5591a', normal, compile, [''])
 test('T5591b', normal, compile, [''])
+test('T7280', normal, compile, [''])