This tool provides basic on-line help for Logtalk features and libraries when running in most operating-systems. For help on the Logtalk compiler error and warning messages, see the tutor tool.

API documentation

This tool API documentation is available at:


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


| ?- logtalk_load(help(loader)).


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

| ?- logtalk_load(help(tester)).

Supported operating-systems

Currently, support is limited to Linux, macOS, and Windows.

On Windows, the start command must be available. On Linux, the xdg-open command must be available. On macOS, the command open is used.

This tool relies on the library portable operating-system access abstraction.


After loading the tool, use the query help::help to get started.

Experimental features

On POSIX systems, when using Ciao Prolog, ECLiPSe, GNU Prolog (1.5.1 or later version), LVM, SICStus Prolog, SWI-Prolog, Trealla Prolog, or XSB as the backend, apis/1 and handbook/0-1 predicates are made available. These predicates open inline at the top-level interpreter the Texinfo versions of the Handbook and the APIs documentation. The optional argument is a starting node, which can be an atom, a predicate indicator, or a non-terminal indicator. When there are several nodes for the same argument (e.g. multiple implementations of the member/2 predicate), one of them will be displayed. Some examples:

| ?- help::handbook.

| ?- help::handbook(base64).

| ?- help::handbook(logtalk_load/2).

| ?- help::apis.

| ?- help::apis(check/2).

| ?- help::apis(message_tokens//2).

Although less useful, you can also browse the man pages of Logtalk scripts. For example:

| ?- help::man(logtalk_tester).

When you finish consult the documentation and quit the info process, you will be back to the top-level prompt (if you find that the top-level have scrolled from its last position, try to set your terminal terminfo to xterm-256colour).

If you’re running Logtalk from a git clone of its repo, you will need to run the scripts/ or scripts/update_html_docs.ps1 scripts to generate the APIs documentation .info file and also run the manuals/sources/ or manuals/sources/build_manuals.ps1 scripts to generated the Handbook .info file. In alternative, you can download the .info files for the latest stable release from the Logtalk website and save them to the docs and manuals directories.

The required info command is provided by the third-party texinfo package (tested with version 6.8). On macOS, this package can be installed with either MacPorts:

$ sudo port install texinfo

Or using Homebrew:

$ brew install texinfo

On Linux systems, use the distribution own package manager to install the texinfo package. For example, in Ubuntu systems:

$ sudo apt install info

Known issues

The open commands used to open documentation URLs drop the fragment part, thus preventing navigating to the specified position on the documentation page.

When browsing the Texinfo versions of the Handbook and the APIs documentation generated with a recent version of Sphinx and using a recent version of Texinfo, the Texinfo search feature often displays the previous nodes of the searched nodes.

ECLiPSe defines a help prefix operator that forces wrapping this atom between parenthesis when sending messages to the tool. E.g. use (help)::help instead of help::help.