X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Debug%2FTrace.hs;h=ebacb6c3d7fa28d37e385a2d240c97b2bd4d8d78;hb=be2750a0a11b919fb03cc070074e430f88bdfa90;hp=5bc71280c9a96c538b8c1c95b62b629fa74a72ad;hpb=de2b563a240bafc20b656729d1ecde0c890d22da;p=ghc-base.git

diff --git a/Debug/Trace.hs b/Debug/Trace.hs
index 5bc7128..ebacb6c 100644
--- a/Debug/Trace.hs
+++ b/Debug/Trace.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP, ForeignFunctionInterface #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Debug.Trace
@@ -13,9 +15,10 @@
 -----------------------------------------------------------------------------
 
 module Debug.Trace (
-	-- * Tracing
-	putTraceMsg,      -- :: String -> IO ()
-	trace             -- :: String -> a -> a
+        -- * Tracing
+        putTraceMsg,      -- :: String -> IO ()
+        trace,            -- :: String -> a -> a
+        traceShow
   ) where
 
 import Prelude
@@ -23,23 +26,27 @@ import System.IO.Unsafe
 
 #ifdef __GLASGOW_HASKELL__
 import Foreign.C.String
+#else
+import System.IO (hPutStrLn,stderr)
 #endif
 
 -- | 'putTraceMsg' function outputs the trace message from IO monad.
--- Usually the output stream is 'stderr' but if the function is called
+-- 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__
-    hPutStr handle msg
-    hPutChar handle '\n'
+    hPutStrLn stderr msg
 #else
     withCString "%s\n" $ \cfmt ->
      withCString msg  $ \cmsg ->
       debugBelch cfmt cmsg
 
-foreign import ccall unsafe debugBelch :: CString -> CString -> IO ()
+-- 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
 
 {-# NOINLINE trace #-}
@@ -55,3 +62,11 @@ trace :: String -> a -> a
 trace string expr = unsafePerformIO $ do
     putTraceMsg string
     return expr
+
+{-|
+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