X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Control%2FConcurrent%2FChan.hs;h=e06e0cb7a237f5636183495ae9aab72ab627d6d2;hb=3310565c512605a71d52f44c4fe645c7ae92786d;hp=dfc46c38cbb3e77342291e2b6b6d1a4fcafb04ac;hpb=1307901a3528834b706eb9336bd0a3ba88fe09f3;p=ghc-base.git

diff --git a/Control/Concurrent/Chan.hs b/Control/Concurrent/Chan.hs
index dfc46c3..e06e0cb 100644
--- a/Control/Concurrent/Chan.hs
+++ b/Control/Concurrent/Chan.hs
@@ -46,6 +46,7 @@ import Data.Typeable
 data Chan a
  = Chan (MVar (Stream a))
         (MVar (Stream a))
+   deriving Eq
 
 INSTANCE_TYPEABLE1(Chan,chanTc,"Chan")
 
@@ -93,6 +94,9 @@ readChan (Chan readVar _) = do
 -- either channel from then on will be available from both.  Hence this creates
 -- a kind of broadcast channel, where data written by anyone is seen by
 -- everyone else.
+--
+-- (Note that a duplicated channel is not equal to its original.
+-- So: @fmap (c /=) $ dupChan c@ returns @True@ for all @c@.)
 dupChan :: Chan a -> IO (Chan a)
 dupChan (Chan _ writeVar) = do
    hole       <- readMVar writeVar