Unsafe.hs

{-
	Copyright (C) 2010 Dr. Alistair Ward

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.
-}
{- |
 [@AUTHOR@]	Dr. Alistair Ward

 [@DESCRIPTION@]

	* Provides impure functions to print & return the specified value.

	* The pure interfaces permit calls from outside the /IO-monad/.

 [@TODO@]	Review function-names.
-}

module ToolShed.Unsafe(
-- * Functions
	print',
	printShow
) where

import qualified	System.IO
import qualified	System.IO.Unsafe

{-# NOINLINE print' #-}
-- | A transparent print-function, for use in debugging.
print' :: Show s
	=> s	-- ^ Arbitrary polymorphic input-data.
	-> s	-- ^ Output (identical to input).
print'	= System.IO.Unsafe.unsafePerformIO . f	where
	f :: Show s => s -> IO s
	f x	= System.IO.hPrint System.IO.stderr x	>> return {-to IO-monad-} x

{-# NOINLINE printShow #-}
-- | A transparent print-function, which prepends the specified label, for use in debugging.
printShow :: Show s
	=> String	-- ^ The label to be printed before the value of the input data.
	-> s		-- ^ Arbitrary polymorphic input-data.
	-> s		-- ^ Output (identical to input).
printShow label	= System.IO.Unsafe.unsafePerformIO . f label	where
	f :: Show s => String -> s -> IO s
	f s x	= System.IO.hPutStrLn System.IO.stderr (s ++ show x)	>> return {-to IO-monad-} x