X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Debug%2FTrace.hs;h=79d44c75b4e3d3b97deb9febb87362d9ada29613;hb=17c3536d93b3d35082ac025bb35176168c359165;hp=993a72e412a338913c5f476ffe4fadeb0fdae52f;hpb=2c19d1a0efd17ab30b773ec3fd88f212af8317b6;p=ghc-base.git

diff --git a/Debug/Trace.hs b/Debug/Trace.hs
index 993a72e..79d44c7 100644
--- a/Debug/Trace.hs
+++ b/Debug/Trace.hs
@@ -1,20 +1,19 @@
 -----------------------------------------------------------------------------
--- 
+-- |
 -- Module      :  Debug.Trace
 -- 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   :  provisional
 -- Portability :  portable
 --
--- $Id: Trace.hs,v 1.2 2002/04/24 16:01:51 simonmar Exp $
---
--- The trace function.
+-- The 'trace' function.
 --
 -----------------------------------------------------------------------------
 
 module Debug.Trace (
+	-- * Tracing
 	trace -- :: String -> a -> a
   ) where
 
@@ -27,15 +26,25 @@ import GHC.IOBase
 import GHC.Handle
 #endif
 
-#ifdef __GLASGOW_HASKELL__
 {-# NOINLINE trace #-}
+{-|
+When called, 'trace' prints the string in its first argument to
+standard error, before returning the second argument as its result.
+The 'trace' function is not referentially transparent, and should only
+be used for debugging, or for monitoring execution. Some
+implementations of 'trace' may decorate the string that\'s output to
+indicate that you\'re tracing.
+-}
 trace :: String -> a -> a
 trace string expr = unsafePerformIO $ do
     hPutStr stderr string
     hPutChar stderr '\n'
+#ifdef __GLASGOW_HASKELL__
     fd <- withHandle_ "trace" stderr $ (return.haFD)
     postTraceHook fd
+#endif
     return expr
 
+#ifdef __GLASGOW_HASKELL__
 foreign import ccall "PostTraceHook" postTraceHook :: Int -> IO ()
 #endif