[project @ 2003-03-08 19:02:39 by panne]

[ghc-base.git] / Debug / Trace.hs

diff --git a/Debug/Trace.hs b/Debug/Trace.hs
index d5a012a..79d44c7 100644 (file)
--- 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 1.1 2001/06/28 14:15:02 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
 
-foreign import "PostTraceHook" postTraceHook :: Int -> IO ()
+#ifdef __GLASGOW_HASKELL__
+foreign import ccall "PostTraceHook" postTraceHook :: Int -> IO ()
 #endif