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This file is part of Logtalk
Copyright 1998-2021 Paulo Moura SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


This tool contains simple wrappers for selected Prolog profiler tools.


This tool can be loaded using the query:

?- logtalk_load(profiler(loader)).

For sample queries, please see the SCRIPT.txt file in the tool directory.


To test this tool, load the tester.lgt file:

| ?- logtalk_load(profiler(tester)).

Supported backend Prolog compilers

Currently, this tool supports the profilers provided with SICStus Prolog 4, SWI-Prolog, and YAP. The tool includes two files:

  • yap_profiler.lgt
    simple wrapper for the YAP count profiler

  • sicstus_profiler.lgt
    simple wrapper for the SICStus Prolog 4 profiler

Logtalk also supports the YAP tick profiler (using the latest YAP development version) and the SWI-Prolog XPCE profiler. When using the XPCE profiler, you can avoid profiling the Logtalk compiler (which is invoked e.g. when you use the ::/2 message-sending operator at the top-level interpreter) by compiling your code with the optimize flag turned on:

?- set_logtalk_flag(optimize, on).

?- use_module(library(statistics)).

?- profile(... :: ...).

Given that prolog_statistics:profile/1 is a meta-predicate, Logtalk will compile its argument before calling it thanks to the goal_expansion/2 hook predicate definitions in the adapter file. Without this hook definition, you would need to use instead (to avoid profiling the compiler itself):

?- logtalk << (prolog_statistics:profile(... :: ...)).

In either case, Don't forget, however, to load the prolog_statistics module before using or compiling calls to the profile/1 to allow the Logtalk compiler to access its meta-predicate template.

The profiler support attempts to conceal internal Logtalk compiler/runtime predicates and the generated entity predicates that implement predicate inheritance. Calls to internal compiler and runtime predicates have functors starting with $lgt_. Calls to predicates with functors such as _def, _dcl, or _super, used to implement inheritance, may still be listed in a few cases. Note that the time and the number of calls/redos of concealed predicates is added to the caller predicates.

Compiling source code for profiling

In order to get user-level object and predicate names instead of compiler generated internal names when using the SWI-Prolog and YAP profilers, you must set code_prefix flag to a character other than the default $ before compiling your source code. For example:

?- set_logtalk_flag(code_prefix, '.').

See also the settings-sample.lgt file for automating the necessary setup at Logtalk startup.