Test Trac #7856

tests/typecheck/should_fail/T7856.hs

@@ -0,0 +1,19 @@
+module T7856 where
+
+tmp :: String -> IO ()
+tmp = sequence_ lst
+  where lst = [putStrLn "hi"]
+
+-- sequence_ :: Monad m => [m a] -> m ()
+
+{-    m () ~ (->) String (IO ())
+      m a  ~ IO ()
+
+Depends which one gets treated first.
+  m := IO 
+is better than
+  m := (->) String
+It's a bit random which is chosen.
+
+I'll put it in regression suite so we see if it wobbles around.
+-}

tests/typecheck/should_fail/T7856.stderr

@@ -0,0 +1,11 @@
+
+T7856.hs:4:7:
+    Couldn't match expected type ‛String -> IO ()’
+                with actual type ‛IO ()’
+    Possible cause: ‛sequence_’ is applied to too many arguments
+    In the expression: sequence_ lst
+    In an equation for ‛tmp’:
+        tmp
+          = sequence_ lst
+          where
+              lst = [putStrLn "hi"]

tests/typecheck/should_fail/all.T

@@ -306,3 +306,4 @@ test('TcNullaryTCFail', when(compiler_lt('ghc', '7.7'), skip), compile_fail, [''
 test('T7857', normal, compile_fail, [''])
 test('T7778', normal, compile_fail, [''])
 test('T7851', normal, compile_fail, [''])
+test('T7856', normal, compile_fail, [''])