[commit: base] master: add test for #5943 (ebcb55d)

[Simon Marlow]

Repository : ssh://darcs.haskell.org//srv/darcs/packages/base

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/ebcb55d5e13f32535b253add2e42db6fe720c2a9

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

commit ebcb55d5e13f32535b253add2e42db6fe720c2a9
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Fri Mar 23 15:00:34 2012 +0000

    add test for #5943

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

 tests/5943.hs     |   36 ++++++++++++++++++++++++++++++++++++
 tests/5943.stdout |    7 +++++++
 tests/all.T       |    2 ++
 3 files changed, 45 insertions(+), 0 deletions(-)

diff --git a/tests/5943.hs b/tests/5943.hs
new file mode 100644
index 0000000..88fa24d
--- /dev/null
+++ b/tests/5943.hs
@@ -0,0 +1,36 @@
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
+import Control.Monad
+import Control.Monad.Fix
+import Data.IORef
+import Prelude hiding (until)
+
+data Phase a = Ready a | Updated a a
+
+delay :: IO Int               -- ^ the signal to delay
+      -> IO (IO (), IO (), IO Int)   -- ^ the delayed signal
+delay s = do
+  ref <- newIORef (Ready 0)
+  let
+      upd = do v <- readIORef ref
+               case v of
+                 Ready x -> do putStrLn "upd: Ready"; x' <- s; putStrLn (show x'); writeIORef ref (Updated x' x)
+                 _       -> return ()
+
+      fin = do v <- readIORef ref
+               case v of
+                 Updated x _ -> do putStrLn "fin: Updated"; writeIORef ref $! Ready x
+                 _           -> error "Signal not updated!"
+
+      sig = do v <- readIORef ref
+               case v of
+                 Ready x     -> do putStrLn "sig: Ready"; return x
+                 Updated _ x -> do putStrLn "sig: Updated"; return x
+
+  return (upd,fin,sig)
+
+main = do
+    (upd,fin,_) <- mfix $ \ ~(_,_,sig) -> delay (fmap (1+) sig)
+    upd
+    fin
+    upd
diff --git a/tests/5943.stdout b/tests/5943.stdout
new file mode 100644
index 0000000..d24cba1
--- /dev/null
+++ b/tests/5943.stdout
@@ -0,0 +1,7 @@
+upd: Ready
+sig: Ready
+1
+fin: Updated
+upd: Ready
+sig: Ready
+2
diff --git a/tests/all.T b/tests/all.T
index 13f25f0..ae00389 100644
--- a/tests/all.T
+++ b/tests/all.T
@@ -116,3 +116,5 @@ test('weak001', normal, compile_and_run, [''])
 #     http://mingw-users.1079350.n2.nabble.com/Bug-re-Unicode-on-the-console-td3121717.html
 test('4006', if_msys(expect_fail), compile_and_run, [''])
 
+test('5943', normal, compile_and_run, [''])
+