Ide.Plugin.Tactic.Debug

Documentation

unsafeRender :: Outputable a => a -> String

Print something

unsafeRender' :: SDoc -> String

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 <- Just 3
    traceM ("x: " ++ show x)
    y <- pure 12
    traceM ("y: " ++ show y)
    pure (x*2 + y)
:}
x: 3
y: 12
Just 18

Since: base-4.7.0.0

traceShowId :: Show a => a -> a

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

>>> traceShowId (1+2+3, "hello" ++ "world")
(6,"helloworld")
(6,"helloworld")

Since: base-4.7.0.0

trace :: String -> a -> a

The trace function outputs the trace message given as its first argument, before returning the second argument as its result.

For example, this returns the value of f x but first outputs the message.

>>> let x = 123; f = show
>>> trace ("calling f with x = " ++ show x) (f x)
"calling f with x = 123
123"

The trace function should only be used for debugging, or for monitoring execution. The function is not referentially transparent: its type indicates that it is a pure function but it has the side effect of outputting the trace message.

traceX :: Show a => String -> a -> b -> b

traceIdX :: Show a => String -> a -> a

traceMX :: (Monad m, Show a) => String -> a -> m ()