# Installing Logtalk

This page provides an overview of Logtalk installation requirements and instructions and a description of the files contained in the Logtalk distribution. For detailed, up-to-date installation and configuration instructions, please see the `README.md`, `INSTALL.md`, and `CUSTOMIZE.md` files distributed with Logtalk. The broad compatibility of Logtalk, both with Prolog compilers and operating-systems, together with all the possible user scenarios, means that installation can vary from very simple, by running an installer or a couple of scripts, to the need of patching both Logtalk and Prolog compilers to workaround the lack of strong Prolog standards or to cope with the requirements of less common operating-systems.

The preferred installation scenario is to have Logtalk installed in a system-wide location, thus available for all users, and a local copy of user-modifiable files on each user home directory (even when you are the single user of your computer). This scenario allows each user to independently customize Logtalk and to freely modify the provided libraries and programming examples. Logtalk installers, installation shell scripts, and Prolog integration scripts favor this installation scenario, although alternative installation scenarios are always possible. The installers set two environment variables, `LOGTALKHOME` and `LOGTALKUSER`, pointing, respectively, to the Logtalk installation folder and to the Logtalk user folder.

User applications should preferably be kept outside of the Logtalk user folder created by the installation process, as updating Logtalk often results in updating the contents of this folder. If your applications depend on customizations to the distribution files, backup those changes before updating Logtalk.

## Hardware and software requirements

### Computer and operating system

Logtalk is compatible with almost any computer/operating-system with a modern, standards-compliant, Prolog compiler available.

### Prolog compiler

Logtalk requires a backend Prolog compiler supporting official and de facto standards. Capabilities needed by Logtalk that are not defined in the official ISO Prolog Core standard include:

- access to predicate properties

- operating-system access predicates

- de facto standard predicates not (yet) specified in the official standard

Logtalk needs access to the predicate property `built_in` to properly compile objects and categories that contain Prolog built-in predicate calls. In addition, some Logtalk built-ins need to know the dynamic/static status of predicates to ensure correct application. The ISO standard for Prolog modules defines a `predicate_property/2` predicate that is already implemented by most Prolog compilers. Note that if these capabilities are not built-in the user cannot easily define them.

For optimal performance, Logtalk requires that the Prolog compiler supports first-argument indexing for both static and dynamic code (most modern compilers support this feature).

Since most Prolog compilers are moving closer to the ISO Prolog standard [ISO95], it is advisable that you try to use the most recent version of your favorite Prolog compiler.

## Logtalk installers

Logtalk installers are available for macOS, Linux, and Microsoft Windows. Depending on the chosen installer, some tasks (e.g., setting environment variables or integrating Logtalk with some Prolog compilers) may need to be performed manually.

## Source distribution

Logtalk sources are available in a `tar` archive compressed with `bzip2`, `lgt3xxx.tar.bz2`. You may expand the archive by using a decompressing utility or by typing the following commands at the command-line:

    % tar -jxvf lgt3xxx.tar.bz2

This will create a sub-directory named `lgt3xxx` in your current directory. Almost all files in the Logtalk distribution are text files. Different operating-systems use different end-of-line codes for text files. Ensure that your decompressing utility converts the end-of-lines of all text files to match your operating system.

## Distribution overview

In the Logtalk installation directory, you will find the following files and directories:

`ACKNOWLEDGMENTS.md` - List of authors, contributors, sponsors, and open source credits

`BIBLIOGRAPHY.bib` – Logtalk bibliography in BibTeX format

`CITATION.cff` - Information on how to cite Logtalk

`CODE_OF_CONDUCT.md` - Code of conduct for contributors and users posting on support forums

`CUSTOMIZE.md` – Logtalk end-user customization instructions

`INSTALL.md` – Logtalk installation instructions

`LICENSE.txt` – Logtalk user license

`NOTICE.txt` – Logtalk copyright notice

`QUICK_START.md` – Quick start instructions for those that do not like to read manuals

`README.md` – several useful pieces of information

`RELEASE_NOTES.md` – release notes for this version

`UPGRADING.md` – instructions on how to upgrade your programs to the current Logtalk version

`VERSION.txt` – file containing the current Logtalk version number (used for compatibility checking when upgrading Logtalk)

`adapters`

  `NOTES.md` – notes on the provided adapter files

  `template.pl` – template adapter file

  `...` – specific adapter files

`coding`

  `NOTES.md` – notes on syntax highlighter and text editor support files providing syntax coloring for publishing and editing Logtalk source code

  `...` – syntax coloring support files

`contributions`

  `NOTES.md` – notes on the user-contributed code

  `...` – user-contributed code files

`core`

  `NOTES.md` – notes on the current status of the compiler and runtime

  `...` – core source files

`docs/apis`

  `NOTES.md` – notes on the provided documentation for core, library, tools, and contributions entities

  `index.html` – root document for all entities documentation

  `...` – other entity documentation files

`docs/handbook`

  `NOTES.md` – notes on the provided documentation

  `bibliography.html` – bibliography

  `glossary.html` – glossary

  `index.html` – root document for all documentation

  `...` – other documentation files

`docs/man`

  `...` – POSIX man pages for the shell scripts

`examples`

  `NOTES.md` – short description of the provided examples

  `ack`

    `NOTES.md` – example notes and sample queries

    `loader.lgt` – loader utility file for the example objects

    `...` – ack example source files

  `...` – other examples

`integration`

  `NOTES.md` – notes on scripts for Logtalk integration with Prolog compilers

  `...` – Prolog integration scripts

`library`

  `NOTES.md` – short description of the library contents

  `all_loader.lgt` – loader utility file for all library entities

  `...` – library source files

`paths`

  `NOTES.md` – description on how to setup library and example paths

  `paths.pl` – default library and example paths

`ports`

  `NOTES.md` – description of included ports of third-party software

  `...` – ports

`samples`

  `loader-sample.lgt` – sample loader file for user applications

  `settings-sample.lgt` – sample file for user-defined Logtalk settings

  `tester-sample.lgt` – sample file for helping to automate running user application unit tests

  `tests-sample.lgt` – sample file for writing user application unit tests

`scratch`

  `NOTES.md` – notes on the scratch directory

`scripts`

  `NOTES.md` – notes on scripts for Logtalk user setup, packaging, and installation

  `...` – packaging, installation, and setup scripts

`tests`

  `NOTES.md` – notes on the current status of the unit tests

  `...` – unit tests for built-in features

`tools`

  `NOTES.md` – notes on the provided programming tools

  `...` – programming tools

### Adapter files

Adapter files provide the glue code between the Logtalk compiler/runtime and a Prolog compiler. Each adapter file contains two sets of predicates: ISO Prolog standard predicates and directives not built-in in the target Prolog compiler and Logtalk specific predicates.

Logtalk already includes ready-to-use adapter files for most academic and commercial Prolog compilers. If an adapter file is not available for the compiler that you intend to use, then you need to build a new one, starting from the included `template.pl` file. Start by making a copy of the template file. Carefully check (or complete if needed) each listed definition. If your Prolog compiler conforms to the ISO standard, this task should only take you a few minutes. In most cases, you can borrow code from the predefined adapter files. If you are unsure that your Prolog compiler provides all the ISO predicates needed by Logtalk, try to run the system by setting the unknown predicate error handler to report as an error any call to a missing predicate. Better yet, switch to a modern, ISO-compliant, Prolog compiler. If you send me your adapter file, with a reference to the target Prolog compiler, maybe I can include it in the next release of Logtalk.

The adapter files specify default values for most of the Logtalk compiler flags. They also specify values for read-only flags that are used to describe Prolog backend-specific features.

### Compiler and runtime

The `core` sub-directory contains the Prolog and Logtalk source files that implement the Logtalk compiler and the Logtalk runtime. The compiler and the runtime may be split in two (or more) separate files or combined into a single file, depending on the Logtalk release that you are installing.

### Library

The Logtalk distribution includes a standard library of useful objects, categories, and protocols. Read the corresponding `NOTES.md` file for details about the library contents.

### Examples

The Logtalk distribution includes a large number of programming examples. The sources of each one of these examples can be found included in a subdirectory with the same name, inside the directory examples. The majority of these examples include tests and a file named `SCRIPT.txt` with sample calls. Some examples may depend on other examples and library objects to work properly. Read the corresponding `NOTES.md` file for details before running an example.

### Logtalk source files

Logtalk source files are text files containing one or more entity definitions (objects, categories, or protocols). The Logtalk source files may also contain plain Prolog code. The extension `.lgt` is normally used. Logtalk compiles these files to plain Prolog by appending to the file name a suffix derived from the extension and by replacing the `.lgt` extension with `.pl` (`.pl` is the default Prolog extension; if your Prolog compiler expects the Prolog source filenames to end with a specific, different extension, you can set it in the corresponding adapter file).