--
-----------------------------------------------------------------------------
-#ifndef __HUGS__
-#include "config.h"
-#endif
-
module Debug.Trace (
-- * Tracing
-
- -- ** Tracers
- -- | The tracer is a function that monitors the trace messages.
- fileTracer, -- :: Handle -> String -> IO ()
-#ifdef mingw32_TARGET_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 System.IO.Unsafe
-import System.IO
#ifdef __GLASGOW_HASKELL__
-import GHC.IOBase
-import GHC.Handle
-#endif
-
import Foreign.C.String
-
-{-# 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_TARGET_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 ()
+#else
+import System.IO (hPutStrLn,stderr)
#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.
+-- 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
- ts <- readIORef tracers
- mapM_ (\(n,l) -> l msg) ts
+#ifndef __GLASGOW_HASKELL__
+ hPutStrLn stderr msg
+#else
+ withCString "%s\n" $ \cfmt ->
+ withCString msg $ \cmsg ->
+ debugBelch cfmt cmsg
+
+foreign import ccall unsafe "RtsMessages.h debugBelch"
+ debugBelch :: CString -> CString -> IO ()
+#endif
{-# 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.
+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
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