Test Trac #10403

testsuite/tests/partial-sigs/should_compile/T10403.hs

+{-# LANGUAGE PartialTypeSignatures #-}
+module T10403 where
+
+data I a = I a
+instance Functor I where
+    fmap f (I a) = I (f a)
+
+newtype B t a = B a
+instance Functor (B t) where
+    fmap f (B a) = B (f a)
+
+newtype H f = H (f ())
+
+app :: H (B t)
+app = h (H . I) (B ())
+
+h :: _ => _
+--h :: Functor m => (a -> b) -> m a -> H m
+h f b = (H . fmap (const ())) (fmap f b)

testsuite/tests/partial-sigs/should_compile/T10403.stderr

+
+T10403.hs:17:6: warning:
+    Found hole ‘_’ with inferred constraints: Functor f
+    In the type signature for ‘h’: _ => _
+
+T10403.hs:17:11: warning:
+    Found hole ‘_’ with type: (a -> b) -> f a -> H f
+    Where: ‘f’ is a rigid type variable bound by
+               the inferred type of h :: Functor f => (a -> b) -> f a -> H f
+               at T10403.hs:19:1
+           ‘b’ is a rigid type variable bound by
+               the inferred type of h :: Functor f => (a -> b) -> f a -> H f
+               at T10403.hs:19:1
+           ‘a’ is a rigid type variable bound by
+               the inferred type of h :: Functor f => (a -> b) -> f a -> H f
+               at T10403.hs:19:1
+    In the type signature for ‘h’: _ => _

testsuite/tests/partial-sigs/should_compile/all.T

@@ -46,3 +46,4 @@ test('SomethingShowable', normal, compile, ['-ddump-types -fno-warn-partial-type
 test('Uncurry', normal, compile, ['-ddump-types -fno-warn-partial-type-signatures'])
 test('UncurryNamed', normal, compile, ['-ddump-types -fno-warn-partial-type-signatures'])
 test('WarningWildcardInstantiations', normal, compile, ['-ddump-types'])
+test('T10403', normal, compile, [''])