add GHC.HetMet.{hetmet_kappa,hetmet_kappa_app}

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

diff --git a/Debug/Trace.hs b/Debug/Trace.hs
index 6f1ce82..ebacb6c 100644 (file)
--- a/Debug/Trace.hs
+++ b/Debug/Trace.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP, ForeignFunctionInterface #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Debug.Trace
@@ -8,32 +10,63 @@
 -- Stability   :  provisional
 -- Portability :  portable
 --
--- The trace function.
+-- The 'trace' function.
 --
 -----------------------------------------------------------------------------
 
 module Debug.Trace (
-       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
+
+-- | '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' 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