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-rw-r--r--tests/examples/ghc86/T3263-2.hs39
1 files changed, 39 insertions, 0 deletions
diff --git a/tests/examples/ghc86/T3263-2.hs b/tests/examples/ghc86/T3263-2.hs
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+++ b/tests/examples/ghc86/T3263-2.hs
@@ -0,0 +1,39 @@
+-- Trac #3263. New kind of warning on monadic bindings that discard a monadic result
+{-# LANGUAGE RankNTypes #-}
+
+module T3263 where
+
+import Control.Monad.Fix
+
+-- No warning
+t1 :: Monad m => m Int
+t1 = do
+ return 10
+
+-- No warning
+t2 :: Monad m => m (m Int)
+t2 = return (return 10)
+
+-- No warning
+t3 :: Monad m => m (m Int)
+t3 = do
+ return 10
+ return (return 10)
+
+-- Warning
+t4 :: forall m. Monad m => m Int
+t4 = do
+ return (return 10 :: m Int)
+ return 10
+
+-- No warning
+t5 :: forall m. Monad m => m Int
+t5 = do
+ _ <- return (return 10 :: m Int)
+ return 10
+
+-- Warning
+t6 :: forall m. MonadFix m => m Int
+t6 = mdo
+ return (return 10 :: m Int)
+ return 10