X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Debug%2FTrace.hs;h=ebacb6c3d7fa28d37e385a2d240c97b2bd4d8d78;hb=HEAD;hp=05809a06b1cb5ca84878aa2f3d102a9bdfdf4f54;hpb=9812e0a321ec0ed8f9e53eb2febfb14c79564200;p=ghc-base.git

diff --git a/Debug/Trace.hs b/Debug/Trace.hs
index 05809a0..ebacb6c 100644
--- a/Debug/Trace.hs
+++ b/Debug/Trace.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP, ForeignFunctionInterface #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Debug.Trace
@@ -13,40 +15,58 @@
 -----------------------------------------------------------------------------
 
 module Debug.Trace (
-	-- * Tracing
-	trace -- :: String -> a -> a
+        -- * Tracing
+        putTraceMsg,      -- :: String -> IO ()
+        trace,            -- :: String -> a -> a
+        traceShow
   ) where
 
 import Prelude
 import System.IO.Unsafe
-import System.IO
 
 #ifdef __GLASGOW_HASKELL__
-import GHC.IOBase
-import GHC.Handle
+import Foreign.C.String
+#else
+import System.IO (hPutStrLn,stderr)
 #endif
 
-#ifdef __HUGS__
-import Hugs.IOExts
+-- | 'putTraceMsg' function outputs the trace message from IO monad.
+-- Usually the output stream is 'System.IO.stderr' but if the function is called
+-- from Windows GUI application then the output will be directed to the Windows
+-- debug console.
+putTraceMsg :: String -> IO ()
+putTraceMsg msg = do
+#ifndef __GLASGOW_HASKELL__
+    hPutStrLn stderr msg
+#else
+    withCString "%s\n" $ \cfmt ->
+     withCString msg  $ \cmsg ->
+      debugBelch cfmt cmsg
+
+-- don't use debugBelch() directly, because we cannot call varargs functions
+-- using the FFI.
+foreign import ccall unsafe "HsBase.h debugBelch2"
+   debugBelch :: CString -> CString -> IO ()
 #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.
+When called, 'trace' outputs the string in its first argument, 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. The function is implemented on
+top of 'putTraceMsg'.
 -}
 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
+{-|
+Like 'trace', but uses 'show' on the argument to convert it to a 'String'.
+
+> traceShow = trace . show
+-}
+traceShow :: (Show a) => a -> b -> b
+traceShow = trace . show