-- Stability : provisional
-- Portability : portable
--
--- The trace function.
+-- The 'trace' function.
--
-----------------------------------------------------------------------------
module Debug.Trace (
+ -- * Tracing
trace -- :: String -> a -> a
) where
#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.
+-}
trace :: String -> a -> a
trace string expr = unsafePerformIO $ do
hPutStr stderr string