[commit: ghc] wip/T14677: WIP: reproduction of bug with slow/wrapper closure (36f1621)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : wip/T14677
Link       : http://ghc.haskell.org/trac/ghc/changeset/36f1621014a86ed1d591802020d9b68499b9783e/ghc

>---------------------------------------------------------------

commit 36f1621014a86ed1d591802020d9b68499b9783e
Author: Gabor Greif <ggreif at gmail.com>
Date:   Thu Jan 25 12:20:30 2018 +0100

    WIP: reproduction of bug with slow/wrapper closure


>---------------------------------------------------------------

36f1621014a86ed1d591802020d9b68499b9783e
 T14677.hs | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/T14677.hs b/T14677.hs
new file mode 100644
index 0000000..3c6dd87
--- /dev/null
+++ b/T14677.hs
@@ -0,0 +1,31 @@
+{-# LANGUAGE ExistentialQuantification #-}
+
+module Main where
+
+import GHC.Event
+
+-- frobbed from GHC.Event.Internal
+data Backend = forall a. Backend {
+      beState :: !a
+
+    , beModifyFd :: a
+                 -> Event    -- old events to watch for ('mempty' for new)
+                 -> Event    -- new events to watch for ('mempty' to delete)
+                 -> IO Bool
+    }
+
+backend :: (a -> Event -> Event -> IO Bool) -> a -> Backend
+backend = flip Backend
+
+{-# NOINLINE be #-}
+be = backend mod ev
+  where mod e0 e1 e2 = do putStrLn "Should be:"
+                          putStrLn "([evtRead],[],[evtWrite])"
+                          putStrLn "Is:"
+                          print (e0, e1, e2)
+                          "([evtRead],[],[evtWrite])" <- pure $ show (e0, e1, e2)
+                          pure $ e0 == evtRead
+        ev = evtRead
+
+main = case be of
+         Backend { beModifyFd = mod, beState = sta } -> mod sta mempty evtWrite >>= print