Documenting Logtalk programs

Logtalk automatically generates a documentation file for each compiled entity (object, protocol, or category) in XML format. Contents of the XML file include the entity name, type, and compilation mode (static or dynamic), the entity relations with other entities, and a description of any declared predicates (name, compilation mode, scope, ...).

The XML documentation files can be enriched with arbitrary user-defined information, either about an entity or about its predicates, by using the two directives described below.

Documenting directives

Logtalk supports two documentation directives for providing arbitrary user-defined information about an entity or a predicate. These two directives complement other Logtalk directives that also provide important documentation information like uses/1, calls/1, or mode/2.

Entity directives

Arbitrary user-defined entity information can be represented using the info/1 directive:

    :- info([
        Key1 is Value1,
        Key2 is Value2,
        ...]).

In this pattern, keys should be atoms and values should be ground terms. The following keys are pre-defined and may be processed specially by Logtalk:

comment

Comment describing entity purpose (an atom).

author

Entity author (an atom).

version

Version number (a number).

date

Date of last modification (formatted as Year/Month/Day).

parameters

Parameter names and descriptions for parametric entities (a list of key-values where both keys and values are atoms).

parnames

Parameter names for parametric entities (a list of atoms; a simpler version of the previous key used when parameter descriptions are deemed unnecessary).

remarks

List of general remarks about the entity using the format Topic - Text. Both the topic and the text must be atoms.

For example:

    :- info([
        version is 2.1,
        author is 'Paulo Moura',
        date is 2000/4/20,
        comment is 'Building representation.',
        diagram is 'UML Class Diagram #312']).

Use only the keywords that make sense for your application and remember that you are free to invent your own keywords.

Predicate directives

Arbitrary user-defined predicate information can be represented using the info/2 directive:

    :- info(Functor/Arity, [
        Key1 is Value1,
        Key2 is Value2,
        ...]).

Keys should be atoms and values should be ground terms. The following keys are pre-defined and may be processed specially by Logtalk:

comment

Comment describing predicate purpose (an atom).

arguments

Names and descriptions of predicate arguments for pretty print output (a list of key-values where both keys and values are atoms).

argnames

Names of predicate arguments for pretty print output (a list of atoms; a simpler version of the previous key used when argument descriptions are deemed unnecessary).

allocation

Objects where we should define the predicate. Some possible values are container, descendants, instances, classes, subclasses, and any.

redefinition

Describes if the predicate can be redefined and in what way. Some possible values are never, free, specialize, call_super_first, call_super_last.

exceptions

List of possible expections throw by the predicate using the format Description - Exception term. The description must be an atom. The exception term must be a non-variable term.

examples

List of typical predicate call examples using the format Description - Predicate call - Variable bindings. The description must be an atom. The predicate call term must be a non-variable term. The variable bindings term uses the format {Variable=Term, ...}. When there are no variable bindings, the success or failure of the predicate call should be represented by {yes} or {no}, respectively.

For example:

    :- info(color/1, [
        comment is 'Table of defined colors.',
        argnames is ['Color'],
        constraint is 'Only a maximum of four visible colors allowed.']).

Use only the keywords that make sense for your application and remember that you are free to invent your own keywords.

Processing and viewing documenting files

The XML documenting files are (by default) automatically generated when you compile a Logtalk entity. For example, assuming the default filename extensions, compiling a sort1.lgt file generates a sort1.pl Prolog file and a sort1.xml XML file. The filename extension for each kind of file can be changed in the config files via the '$lgt_file_extension'/2 predicate.

Each XML file contains references to two other files, a XML specification file and a XSL style-sheet file. The XML specification file can be either a DTD file (logtalk.dtd) or a XML Scheme file (logtalk.xsd). The XSL style-sheet file is responsible for converting the XML files to some desired format such as HTML or PDF. The default names for the XML specification file and the XSL style-sheet file are defined in the configuration files. The xml sub-directory in the Logtalk installation directory contains the XML specification files described above, along with several sample XSL style-sheet files and sample scripts for converting XML documenting files to several formats. Please read the NOTES file included in the directory for details. You may use the supplied sample files as a starting point for generating the documentation of your Logtalk applications.

There is a set of compilers options, used with the Logtalk logtalk_load/2 or the logtalk_compile/2 built-in predicates, that can be used to control the generation of the XML documentation files. Please see the Running Logtalk section of this manual for details.