The tracet 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.

tracet ("calling f with x = " <> showt x) (f x)

The tracet 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

Like tracet but accepts a lazy Text argument.

Since: 2

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

Since: 2

Like tracetId but accepts a lazy Text argument.

Since: 2

Like tracet, but uses showt on the argument to convert it to a Text.

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 =
    traceTextShow (x, z) $ result
  where
    z = ...
    ...

Since: 2

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

Since: 2

Like tracet but additionally prints a call stack if one is available.

In the current GHC implementation, the call stack is only availble if the program was compiled with -prof; otherwise tracetStack behaves exactly like tracet. 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

Like tracetStack but accepts a lazy Text argument.

Since: 2

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

Since: 2

Like tracetIO but accepts a lazy Text argument.

Since: 2

Like tracet but returning unit in an arbitrary Applicative context. Allows for convenient use in do-notation. Note that the application of tracet is not an action in the Applicative context, as tracetIO is in the IO type.

... = do
  x <- ...
  tracetM $ "x: " <> showt x
  y <- ...
  tracetM $ "y: " <> showt y

Since: 2

Like tracetM but accepts a lazy Text argument.

Like tracetM, but uses showt on the argument to convert it to a Text.

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

Since: 2

The tracetEvent function behaves like tracet 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 tracetEventIO 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 traceEvent.

Since: 2

Like tracetEvent but accepts a lazy Text argument.

Since: 2

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

Compared to tracetEvent, tracetEventIO sequences the event with respect to other IO actions.

Since: 2

Like tracetEventIO but accepts a lazy Text argument.

Since: 2

The tracetMarker function emits a marker to the eventlog, if eventlog profiling is available and enabled at runtime. The Text 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 tracetMarkerIO 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 traceMarker.

Since: 2

Like tracetMarker but accepts a lazy Text argument.

Since: 2

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

Compared to tracetMarker, tracetMarkerIO sequences the event with respect to other IO actions.

Since: 2

Like tracetMarkerIO but accepts a lazy Text argument.

Since: 2