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------------------------------------------------------------------------------ --- This library contains some useful operation for debugging programs. --- --- @author Bjoern Peemoeller --- @version September 2014 --- @category general ------------------------------------------------------------------------------ module Debug ( trace, traceId, traceShow, traceShowId, traceIO , assert, assertIO ) where import IO (hPutStrLn, stderr) import Unsafe (unsafePerformIO) --- Prints the first argument as a side effect and behaves as identity on the --- second argument. trace :: String -> a -> a trace s x = unsafePerformIO (traceIO s >> return x) --- Prints the first argument as a side effect and returns it afterwards. traceId :: String -> String traceId a = trace a a --- Prints the first argument using `show` and returns the second argument --- afterwards. traceShow :: Show a => a -> b -> b traceShow a b = trace (show a) b --- Prints the first argument using `show` and returns it afterwards. traceShowId :: Show a => a -> a traceShowId a = trace (show a) a --- Output a trace message from the `IO` monad. traceIO :: String -> IO () traceIO m = hPutStrLn stderr m --- Assert a condition w.r.t. an error message. --- If the condition is not met it fails with the given error message, --- otherwise the third argument is returned. assert :: Bool -> String -> a -> a assert cond s x = if cond then x else error s --- Assert a condition w.r.t. an error message from the `IO` monad. --- If the condition is not met it fails with the given error message. assertIO :: Bool -> String -> IO () assertIO cond s = unless cond $ error s |