Use explicit language extensions & remove extension fields from base.cabal

[ghc-base.git] / Control / Concurrent / Chan.hs

diff --git a/Control/Concurrent/Chan.hs b/Control/Concurrent/Chan.hs
index 12f75c9..2255c4e 100644 (file)
--- a/Control/Concurrent/Chan.hs
+++ b/Control/Concurrent/Chan.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Control.Concurrent.Chan
@@ -46,6 +48,7 @@ import Data.Typeable
 data Chan a
  = Chan (MVar (Stream a))
         (MVar (Stream a))
+   deriving Eq
 
 INSTANCE_TYPEABLE1(Chan,chanTc,"Chan")
 
@@ -93,6 +96,9 @@ 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
@@ -106,6 +112,7 @@ unGetChan (Chan readVar _) val = do
    modifyMVar_ readVar $ \read_end -> do
      putMVar new_read_end (ChItem val read_end)
      return new_read_end
+{-# DEPRECATED unGetChan "if you need this operation, use Control.Concurrent.STM.TChan instead.  See http://hackage.haskell.org/trac/ghc/ticket/4154 for details" #-}
 
 -- |Returns 'True' if the supplied 'Chan' is empty.
 isEmptyChan :: Chan a -> IO Bool
@@ -114,6 +121,7 @@ isEmptyChan (Chan readVar writeVar) = do
      w <- readMVar writeVar
      let eq = r == w
      eq `seq` return eq
+{-# DEPRECATED isEmptyChan "if you need this operation, use Control.Concurrent.STM.TChan instead.  See http://hackage.haskell.org/trac/ghc/ticket/4154 for details" #-}
 
 -- Operators for interfacing with functional streams.