[project @ 2005-01-28 13:36:25 by simonmar]

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

diff --git a/Debug/Trace.hs b/Debug/Trace.hs
index 79dcceb..b442a11 100644 (file)
--- a/Debug/Trace.hs
+++ b/Debug/Trace.hs
@@ -2,40 +2,99 @@
 -- |
 -- 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 1.3 2002/04/24 16:31:43 simonmar Exp $
---
--- The trace function.
+-- The 'trace' function.
 --
 -----------------------------------------------------------------------------
 
+#ifdef __GLASGOW_HASKELL__
+#include "ghcconfig.h"
+#endif
+
 module Debug.Trace (
-       trace -- :: String -> a -> a
+       -- * Tracing
+       
+       -- ** Tracers
+       -- | The tracer is a function that monitors the trace messages.
+       fileTracer,       -- :: Handle -> String -> IO ()
+#ifdef mingw32_HOST_OS
+       winDebugTracer,   -- :: String -> IO ()
+#endif
+       addTracer,        -- :: String -> (String -> IO ()) -> IO ()
+       removeTracer,     -- :: String -> IO ()
+       
+       -- ** Messages
+       putTraceMsg,      -- :: String -> IO ()
+       trace             -- :: String -> a -> a
   ) where
 
 import Prelude
+import Data.IORef
 import System.IO.Unsafe
 import System.IO
 
-#ifdef __GLASGOW_HASKELL__
-import GHC.IOBase
-import GHC.Handle
+#ifdef mingw32_HOST_OS
+import Foreign.C.String
 #endif
 
-#ifdef __GLASGOW_HASKELL__
+{-# NOINLINE tracers #-}
+tracers :: IORef [(String, String -> IO ())]
+tracers = unsafePerformIO (newIORef [("defaultTracer", fileTracer stderr)])
+
+-- | A tracer function that outputs the message to a file
+fileTracer :: Handle     -- ^ file handle
+           -> String     -- ^ trace message
+           -> IO ()
+fileTracer handle msg = do
+   hPutStr handle msg
+   hPutChar handle '\n'
+
+#ifdef mingw32_HOST_OS
+-- | A tracer function that outputs the message to the debuger (Windows only)
+winDebugTracer :: String  -- ^ trace message
+               -> IO ()
+winDebugTracer msg = do
+   withCString (msg++"\n") outputDebugString
+
+foreign import ccall unsafe "OutputDebugStringA"
+  outputDebugString :: CString -> IO ()
+#endif
+
+-- | Registering a new tracer
+addTracer :: String             -- ^ the tracer name
+          -> (String -> IO ())  -- ^ tracer
+          -> IO ()
+addTracer name tracer = do
+       ts <- readIORef tracers
+       writeIORef tracers ((name,tracer):filter (\(n,l) -> n /= name) ts)
+
+-- | Removing the tracer with the given name
+removeTracer :: String -> IO ()
+removeTracer name = do
+       ts <- readIORef tracers
+       writeIORef tracers (filter (\(n,l) -> n /= name) ts)
+
+-- | 'putTraceMsg' function outputs the trace message from IO monad.
+putTraceMsg :: String -> IO ()
+putTraceMsg msg = do
+       ts <- readIORef tracers
+       mapM_ (\(n,l) -> l msg) ts
+
 {-# NOINLINE trace #-}
+{-|
+When called, 'trace' outputs the string in its first argument using the
+installed tracers, 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'
-    fd <- withHandle_ "trace" stderr $ (return.haFD)
-    postTraceHook fd
+    putTraceMsg string
     return expr
-
-foreign import ccall "PostTraceHook" postTraceHook :: Int -> IO ()
-#endif