X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Debug%2FTrace.hs;h=742044e4d4c3e1eef013234f23d92500c260a852;hb=8aca076f0de902842f6c5df7322ba42d4664fce4;hp=3e369f5e183c12f728ba0b1534276f33a0325310;hpb=66bcbe67b61d83cb01b6d2c876e7b06e034fba88;p=ghc-base.git

diff --git a/Debug/Trace.hs b/Debug/Trace.hs
index 3e369f5..742044e 100644
--- a/Debug/Trace.hs
+++ b/Debug/Trace.hs
@@ -13,9 +13,10 @@
 -----------------------------------------------------------------------------
 
 module Debug.Trace (
-	-- * Tracing
-	putTraceMsg,      -- :: String -> IO ()
-	trace             -- :: String -> a -> a
+        -- * Tracing
+        putTraceMsg,      -- :: String -> IO ()
+        trace,            -- :: String -> a -> a
+        traceShow
   ) where
 
 import Prelude
@@ -28,7 +29,7 @@ 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 ()
@@ -40,7 +41,10 @@ putTraceMsg msg = do
      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 #-}
@@ -56,3 +60,11 @@ 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