X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Control%2FConcurrent%2FChan.hs;h=1b89f29e3e185717ea358b5cc1502f694f16ed3e;hb=db57e8fc131e5f1507474bb1b38fa7179e494aa0;hp=099213782ddf6472ae4397faa1ad473415485703;hpb=9fa9bc17072a58c0bae2cce4764d38677e96ac29;p=haskell-directory.git

diff --git a/Control/Concurrent/Chan.hs b/Control/Concurrent/Chan.hs
index 0992137..1b89f29 100644
--- a/Control/Concurrent/Chan.hs
+++ b/Control/Concurrent/Chan.hs
@@ -2,37 +2,33 @@
 -- |
 -- Module      :  Control.Concurrent.Chan
 -- Copyright   :  (c) The University of Glasgow 2001
--- License     :  BSD-style (see the file libraries/core/LICENSE)
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
 -- 
 -- Maintainer  :  libraries@haskell.org
 -- Stability   :  experimental
--- Portability :  non-portable
+-- Portability :  non-portable (concurrency).
 --
--- $Id: Chan.hs,v 1.2 2002/04/24 16:31:37 simonmar Exp $
---
--- Standard, unbounded channel abstraction.
+-- Unbounded channels.
 --
 -----------------------------------------------------------------------------
 
 module Control.Concurrent.Chan
-	( Chan			-- abstract
-
-	  -- creator
-	, newChan	 	-- :: IO (Chan a)
-
-	  -- operators
-	, writeChan	 	-- :: Chan a -> a -> IO ()
-	, readChan	 	-- :: Chan a -> IO a
-	, dupChan	 	-- :: Chan a -> IO (Chan a)
-	, unGetChan		-- :: Chan a -> a -> IO ()
-
-	, isEmptyChan		-- :: Chan a -> IO Bool
-
-	  -- stream interface
-	, getChanContents	-- :: Chan a -> IO [a]
-	, writeList2Chan	-- :: Chan a -> [a] -> IO ()
-
-       ) where
+  ( 
+	  -- * The 'Chan' type
+	Chan,			-- abstract
+
+	  -- * Operations
+	newChan,	 	-- :: IO (Chan a)
+	writeChan,	 	-- :: Chan a -> a -> IO ()
+	readChan,	 	-- :: Chan a -> IO a
+	dupChan,	 	-- :: Chan a -> IO (Chan a)
+	unGetChan,		-- :: Chan a -> a -> IO ()
+	isEmptyChan,		-- :: Chan a -> IO Bool
+
+	  -- * Stream interface
+	getChanContents,	-- :: Chan a -> IO [a]
+	writeList2Chan,		-- :: Chan a -> [a] -> IO ()
+   ) where
 
 import Prelude
 
@@ -43,6 +39,7 @@ import Control.Concurrent.MVar
 -- of the channel contents,i.e.,  the read- and write ends. Empty @MVar@s
 -- are used to handle consumers trying to read from an empty channel.
 
+-- |'Chan' is an abstract type representing an unbounded FIFO channel.
 data Chan a
  = Chan (MVar (Stream a))
         (MVar (Stream a))
@@ -57,6 +54,7 @@ data ChItem a = ChItem a (Stream a)
 -- @newChan@ sets up the read and write end of a channel by initialising
 -- these two @MVar@s with an empty @MVar@.
 
+-- |Build and returns a new instance of 'Chan'.
 newChan :: IO (Chan a)
 newChan = do
    hole  <- newEmptyMVar
@@ -69,6 +67,7 @@ newChan = do
 -- filled in with a new stream element holding the entered value and the
 -- new hole.
 
+-- |Write a value to a 'Chan'.
 writeChan :: Chan a -> a -> IO ()
 writeChan (Chan _read write) val = do
   new_hole <- newEmptyMVar
@@ -76,6 +75,7 @@ writeChan (Chan _read write) val = do
     putMVar old_hole (ChItem val new_hole)
     return new_hole
 
+-- |Read the next value from the 'Chan'.
 readChan :: Chan a -> IO a
 readChan (Chan read _write) = do
   modifyMVar read $ \read_end -> do
@@ -84,12 +84,17 @@ readChan (Chan read _write) = do
 	-- else dupChan doesn't work
     return (new_read_end, val)
 
+-- |Duplicate a 'Chan': the duplicate channel begins empty, but data written to
+-- 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.
 dupChan :: Chan a -> IO (Chan a)
 dupChan (Chan _read write) = do
    hole     <- readMVar write
    new_read <- newMVar hole
    return (Chan new_read write)
 
+-- |Put a data item back onto a channel, where it will be the next item read.
 unGetChan :: Chan a -> a -> IO ()
 unGetChan (Chan read _write) val = do
    new_read_end <- newEmptyMVar
@@ -97,6 +102,7 @@ unGetChan (Chan read _write) val = do
      putMVar new_read_end (ChItem val read_end)
      return new_read_end
 
+-- |Returns 'True' if the supplied 'Chan' is empty.
 isEmptyChan :: Chan a -> IO Bool
 isEmptyChan (Chan read write) = do
    withMVar read $ \r -> do
@@ -106,6 +112,8 @@ isEmptyChan (Chan read write) = do
 
 -- Operators for interfacing with functional streams.
 
+-- |Return a lazy list representing the contents of the supplied
+-- 'Chan', much like 'System.IO.hGetContents'.
 getChanContents :: Chan a -> IO [a]
 getChanContents ch
   = unsafeInterleaveIO (do
@@ -114,6 +122,6 @@ getChanContents ch
     	return (x:xs)
     )
 
--------------
+-- |Write an entire list of items to a 'Chan'.
 writeList2Chan :: Chan a -> [a] -> IO ()
 writeList2Chan ch ls = sequence_ (map (writeChan ch) ls)