Logtalk is compatible with almost any computer/operating system with a modern Prolog compiler available. Currently, the main development environment is an Apple PowerBook running MacOS X. Being written in Prolog and distributed in source form, the only issue regarding operating system compatibility are the end-of-line codes in the source text files! Most example source file names do not fit in the 8+3 MS-DOS file length limitation, so this may prevent those examples from running under this operating system (or in any other system with similar limitations).
In writing Logtalk I have tried to follow the recently approved Prolog ISO standard whenever possible. Capabilities needed by Logtalk that are not defined in the ISO standard are:
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<li>access to predicate properties (<code>dynamic</code>, <code>static</code>, <code>built_in</code>)</li>
Logtalk needs access to the predicate property <code>built_in</code> to properly compile objects and categories that contain Prolog built-in predicates 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 <code>predicate_property/2</code> predicate that is already implemented by most Prolog compilers. Note that if these capabilities are not built-in the user cannot easily define them.</p>
For optimal performance, Logtalk requires that the Prolog compiler supports <strong>first-argument indexing</strong> for both static and dynamic code (most modern compilers support this feature).
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Since most Prolog compilers are moving closer to the ISO Prolog standard <ahref="../bibliography.html#ISO95">[ISO 95]</a>, it is advisable that you try to use a recent version of your favorite Prolog compiler.
The Logtalk system can be installed in any directory that is accessible to the user. The installation process consists merely in decompressing an archive file that will lead to a new directory with the structure/contents described below. The decompression process naturally depends on the operative system that you are using. For some operating systems, an installer may be provided. Users wishing to use the Logtalk library and Logtalk examples will need write access to the respective directories or to make a local copy these directories on their home directories. See the file <code>INSTALL</code> for details. The directory <code>scripts</code> may contain scripts for helping with Logtalk packaging, installation, and integration with Prolog compilers.
The Macintosh version is included in the file <code>lgt2xxx.sit</code>, a StuffIt archive. Drag and drop the <code>.sit</code> file in a utility like <code>StuffIt Expander</code> for expanding it.
The MacOS X/BSD/Linux/Unix version is included in the file <code>lgt2xxx.tgz</code>. In order to decompress and install the system you may use the following commands:
The OS/2 and Windows 95/98/NT/ME/2000/XP version is included in the file <code>lgt2xxx.zip</code>. The file can be decompressed using an utility like <code>unzip</code>:
Almost all files in the Logtalk distribution are text files. The only difference between the source files, other than the compressing formats, is the end-of-line codes: Macintosh uses a carriage return, Unix uses a line feed, OS/2 and Windows uses both a carriage return and a line feed. This should make it easier to install Logtalk under other operating systems.
Configuration files provide the glue code between the Logtalk preprocessor/runtime and a Prolog compiler. Each configuration 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 configuration files for most academic and commercial Prolog compilers. If a configuration file is not available for the compiler that you intend to use, then you need to build a new one, starting from the included <code>template.config</code> 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 some of the predefined configuration 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 configuration file, with a reference to the target Prolog compiler, maybe I can include it in the next release of Logtalk.
The configuration files specifies default values for all the Logtalk compiler flags. Most of these compiler flags are described in the <ahref="running.html#options">next</a> section. A few of these flags have read-only values which cannot be changed at runtime. These are:
<dd>Controls the messages printed by Logtalk at startup. Possible flag values are <code>flags</code> (the usual default; prints the Logtalk banner and a list of all compiler flag values), <code>banner</code> (prints only the Logtalk banner), and <code>none</code> (suppress all startup messages; useful for batch processing).</dd>
<dd>Allows the use of alternative directories for storing the Prolog files and the XML documenting files resulting from entity compilation. This flag can only be set for Prolog compilers providing the necessary operating-system access predicates for implementing this feature (specifically, a built-in predicate for creating new directories). Possible option values are <code>on</code> and <code>off</code> (the usual default). The names of the alternative directories are specified using a predicate which is also defined in the configuration files.</dd>
<dd>Informs Logtalk if the Prolog compiler supports the <code>initialization/1</code> directive as specified in the ISO standard. Note that some Prolog compilers support this directive but without the ISO specified semantics. Possible flag values are <code>true</code> and <code>false</code>.</dd>
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<dt><code>supports_break_predicate</code></dt>
<dd>Informs Logtalk if the Prolog compiler supports a <code>break/0</code> predicate (which can be used by the Logtalk built-in debugger). Possible flag values are <code>true</code> and <code>false</code>.</dd>
The <code>compiler</code> sub-directory contains the Prolog source file(s) that implement the Logtalk preprocessor/compiler and the Logtalk runtime. The compiler and the runtime may be split in two (or more) separate files or combined in a single file, depending on the Logtalk release that you are installing.
Starting from version 2.7, Logtalk contains a standard library of useful objects, categories, and protocols. Read the corresponding <code>NOTES</code> file for details about the library contents.
Logtalk 2.x contains new implementations of some of the examples provided with previous 1.x versions. 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 a file named <code>SCRIPT</code> that contains cases of simple utilization. Some examples may depend on other examples and library objects to work properly. Read the corresponding <code>NOTES</code> file for details before running an example.
Each Logtalk entity (object, category or protocol) is contained in a text file named after the entity. The extension <code>.lgt</code> is normally used. The Logtalk preprocessor compiles these files to plain Prolog, replacing the <code>.lgt</code> extension with <code>.pl</code> (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 configuration file.
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