Test Trac #2494

testsuite/tests/ghc-regress/typecheck/should_compile/T2494-2.hs

+{-# LANGUAGE Rank2Types, ScopedTypeVariables #-}
+
+-- Trac #2494, should compile ok
+
+module Foo where
+
+foo :: (forall m. Monad m => Maybe (m a) -> Maybe (m a)) -> Maybe a -> Maybe a
+foo _ x = x
+
+{-# RULES
+
+"foo/foo"
+  forall (f :: forall m. Monad m => Maybe (m a) -> Maybe (m a))
+         (g :: forall m. Monad m => Maybe (m a) -> Maybe (m a)) x.
+  foo f (foo g x) = foo (f . g) x
+ #-}

testsuite/tests/ghc-regress/typecheck/should_compile/T2494.hs

+{-# LANGUAGE Rank2Types, ScopedTypeVariables #-}
+
+-- Trac #2494, should generate an error message
+
+module Foo where
+
+foo :: (forall m. Monad m => Maybe (m a) -> Maybe (m a)) -> Maybe a -> Maybe a
+foo _ x = x
+
+{-# RULES
+
+"foo/foo"
+  forall (f :: forall m. Monad m => Maybe (m a) -> Maybe (m a))
+         (g :: forall m. Monad m => Maybe (m b) -> Maybe (m b)) x.
+  foo f (foo g x) = foo (f . g) x
+ #-}

testsuite/tests/ghc-regress/typecheck/should_compile/T2494.stderr

+
+T2494.hs:12:13:
+    Couldn't match expected type `a' against inferred type `b'
+      `a' is a rigid type variable bound by
+          the type signature for `f' at T2494.hs:10:45
+      `b' is a rigid type variable bound by
+          the type signature for `g' at T2494.hs:11:45
+      Expected type: Maybe (m a)
+      Inferred type: Maybe (m b)
+    In the first argument of `foo', namely `g'
+    In the second argument of `foo', namely `(foo g x)'
+
+T2494.hs:12:29:
+    Couldn't match expected type `a' against inferred type `b'
+      `a' is a rigid type variable bound by
+          the type signature for `f' at T2494.hs:10:45
+      `b' is a rigid type variable bound by
+          the type signature for `g' at T2494.hs:11:45
+      Expected type: Maybe (m a)
+      Inferred type: Maybe (m b)
+    In the second argument of `(.)', namely `g'
+    In the first argument of `foo', namely `(f . g)'
+
+T2494.hs:12:32:
+    Couldn't match expected type `b' against inferred type `a'
+      `b' is a rigid type variable bound by
+          the type signature for `g' at T2494.hs:11:45
+      `a' is a rigid type variable bound by
+          the type signature for `f' at T2494.hs:10:45
+      Expected type: Maybe b
+      Inferred type: Maybe a
+    In the second argument of `foo', namely `x'
+    When checking the transformation rule "foo/foo"

testsuite/tests/ghc-regress/typecheck/should_compile/all.T

@@ -275,6 +275,8 @@ test('T2045', normal, compile, [''])   # Needs -fhpc
 test('T2478', normal, compile, ['']) 
 test('T2433', extra_clean(['T2433_Help.hi', 'T2433_Help.o']), 
      multimod_compile, ['T2433', '-v0'])
+test('T2494', normal, compile_fail, ['']) 
+test('T2494-2', normal, compile, ['']) 
      
 
 # Omitting temporarily