The pTrace function pretty prints 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.

pTrace ("calling f with x = " ++ show x) (f x)

The pTrace 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.

Since: 2.0.1.0

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

Since: 2.0.1.0

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

This makes it convenient for printing the values of interesting variables or expressions inside a function. For example here we print the value of the variables x and z:

f x y =
    pTraceShow (x, z) $ result
  where
    z = ...
    ...

Since: 2.0.1.0

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

Since: 2.0.1.0

The pTraceIO function outputs the trace message from the IO monad. This sequences the output with respect to other IO actions.

Since: 2.0.1.0

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

Note that the application of pTraceM is not an action in the Applicative context, as pTraceIO 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 . pTraceIO may be a better option.

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

Since: 2.0.1.0

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

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

Since: 2.0.1.0

like pTrace, but additionally prints a call stack if one is available.

In the current GHC implementation, the call stack is only available if the program was compiled with -prof; otherwise pTraceStack behaves exactly like pTrace. Entries in the call stack correspond to SCC annotations, so it is a good idea to use -fprof-auto or -fprof-auto-calls to add SCC annotations automatically.

Since: 2.0.1.0

The pTraceEvent function behaves like trace with the difference that the message is emitted to the eventlog, if eventlog profiling is available and enabled at runtime.

It is suitable for use in pure code. In an IO context use pTraceEventIO instead.

Note that when using GHC's SMP runtime, it is possible (but rare) to get duplicate events emitted if two CPUs simultaneously evaluate the same thunk that uses pTraceEvent.

Since: 2.0.1.0

The pTraceEventIO function emits a message to the eventlog, if eventlog profiling is available and enabled at runtime.

Compared to pTraceEvent, pTraceEventIO sequences the event with respect to other IO actions.

Since: 2.0.1.0

The pTraceMarker function emits a marker to the eventlog, if eventlog profiling is available and enabled at runtime. The String is the name of the marker. The name is just used in the profiling tools to help you keep clear which marker is which.

This function is suitable for use in pure code. In an IO context use pTraceMarkerIO instead.

Note that when using GHC's SMP runtime, it is possible (but rare) to get duplicate events emitted if two CPUs simultaneously evaluate the same thunk that uses pTraceMarker.

Since: 2.0.1.0

The pTraceMarkerIO function emits a marker to the eventlog, if eventlog profiling is available and enabled at runtime.

Compared to pTraceMarker, pTraceMarkerIO sequences the event with respect to other IO actions.

Since: 2.0.1.0

Similar to pTrace, but without color.

>>> pTraceNoColor "wow" ()
wow
()

Since: 2.0.2.0

Similar to pTraceId, but without color.

>>> pTraceIdNoColor "(1, 2, 3)" `seq` ()
( 1
, 2
, 3
)
()

Since: 2.0.2.0

Similar to pTraceShow, but without color.

>>> import qualified Data.Map as M
>>> pTraceShowNoColor (M.fromList [(1, True)]) ()
fromList
    [
        ( 1
        , True
        )
    ]
()

Since: 2.0.2.0

Similar to pTraceShowId, but without color.

>>> import qualified Data.Map as M
>>> pTraceShowIdNoColor (M.fromList [(1, True)]) `seq` ()
fromList
    [
        ( 1
        , True
        )
    ]
()

Since: 2.0.2.0

Similar to pTraceM, but without color.

>>> pTraceMNoColor "wow"
wow

Since: 2.0.2.0

Similar to pTraceShowM, but without color.

>>> pTraceShowMNoColor [1,2,3]
[ 1
, 2
, 3
]

Since: 2.0.2.0

Similar to pTraceStack, but without color.

>>> pTraceStackNoColor "wow" () `seq` ()
wow
()

Since: 2.0.2.0

Similar to pTraceEvent, but without color.

Since: 2.0.2.0

Similar to pTraceEventIO, but without color.

Since: 2.0.2.0

Similar to pTraceMarker, but without color.

Since: 2.0.2.0

Similar to pTraceMarkerIO, but without color.

Since: 2.0.2.0

Similar to pTraceIO, but without color.

>>> pTraceIONoColor "(1, 2, 3)"
( 1
, 2
, 3
)

Since: 2.0.2.0