base-compat-0.9.3: A compatibility layer for base

Debug.Trace.Compat

Synopsis

Documentation

Like trace but returns the message instead of a third value.

Since: 4.7.0.0

traceShowId :: Show a => a -> a #

Like traceShow but returns the shown value instead of a third value.

Since: 4.7.0.0

traceM :: Applicative f => String -> f () #

Like trace but returning unit in an arbitrary Applicative context. Allows for convenient use in do-notation.

Note that the application of traceM is not an action in the Applicative context, as traceIO is in the IO type. While the fresh bindings in the following example will force the traceM expressions to be reduced every time the do-block is executed, traceM "not crashed" would only be reduced once, and the message would only be printed once. If your monad is in MonadIO, liftIO . traceIO may be a better option.

... = do
x <- ...
traceM $"x: " ++ show x y <- ... traceM$ "y: " ++ show y

Since: 4.7.0.0

traceShowM :: (Show a, Applicative f) => a -> f () #

Like traceM, but uses show on the argument to convert it to a String.

... = do
x <- ...
traceShowM $x y <- ... traceShowM$ x + y

Since: 4.7.0.0