# Documenting

Assuming that the source_data flag is turned on, the compiler saves all relevant documenting information collected when compiling a source file. The provided lgtdoc tool can access this information by using the reflection support and generate 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 in the next section. The `lgtdoc` tool includes POSIX and Windows scripts for converting the XML documentation files to several final formats (such as HTML and PDF).

## Documenting directives

Logtalk supports two documentation directives for providing arbitrary user-defined information about an entity or a predicate. These two directives complement other directives that also provide important documentation information such as the mode/2 and meta_predicate/1 directives.

### 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 bound terms. The following keys are predefined and may be processed specially by Logtalk tools:

`comment`

  Comment describing the entity purpose (an atom). As a style guideline, don’t use overly long comments. If you need to provide additional details, use the `remarks` key.

`author`

  Entity author(s) (an atom or a compound term `{entity}` where `entity` is the name of an XML entity in a user defined `custom.ent` file).

`version`

  Version number (a `Major:Minor:Patch` compound term) Following the Semantic Versioning guidelines is strongly advised.

`date`

  Date of last modification in ISO 8601 standard format (`Year-Month-Day` where `Year`, `Month`, and `Day` are integers).

`parameters`

  Parameter names and descriptions for parametric entities (a list of `Name-Description` pairs where both names and descriptions 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).

`copyright`

  Copyright notice for the entity source code (an atom or a compound term `{entity}` where `entity` is the name of an XML entity defined in a user defined `custom.ent` file).

`license`

  License terms for the entity source code; usually, just the license name (an atom or a compound term `{entity}` where `entity` is the name of an XML entity in a user defined `custom.ent` file).

`remarks`

  List of general remarks about the entity using `Topic-Text` pairs where both the topic and the text must be atoms.

`see_also`

  List of related entities (using the entity identifiers, which can be atoms or compound terms).

For example:

    :- info([
        version is 2:1:0,
        author is 'Paulo Moura',
        date is 2000-11-20,
        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. All key-value pairs can be retrieved programmatically using the reflection API and are visible to the lgtdoc tool.

### Predicate directives

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

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

The first argument can also a grammar rule non-terminal indicator, `Name//Arity`. Keys should be atoms and values should be bound terms. The following keys are predefined and may be processed specially by Logtalk tools:

`comment`

  Comment describing the predicate (or non-terminal) purpose (an atom). As a style guideline, don’t use overly long comments. If you need to provide additional details, use the `remarks` key.

`arguments`

  Names and descriptions of predicate arguments for pretty print output (a list of `Name-Description` pairs where both names and descriptions 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 predicate is expected to be redefined and, if so, in what way. Some possible values are `never`, `free`, `specialize`, `call_super_first`, `call_super_last`.

`exceptions`

  List of possible exceptions throw by the predicate using `Description-Exception` pairs. The description must be an atom. The exception term must be a ground term.

`examples`

  List of typical predicate call examples using the format `Description-Goal-Bindings`. The description must be an atom with the goal sharing variables with the bindings. 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 the terms `{yes}` or `{no}`, respectively.

`remarks`

  List of general remarks about the predicate using `Topic-Text` pairs where both the topic and the text must be atoms.

For example:

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

As with the `info/1` directive, use only the keywords that make sense for your application and remember that you are free to invent your own keywords. All key-value pairs can also be retrieved programmatically using the reflection API and are visible to the lgtdoc tool.

## Processing and viewing documenting files

The lgtdoc tool generates an XML documenting file per entity. It can also generate library, directory, entity, and predicate indexes when documenting libraries and directories. For example, assuming the default filename extensions, a `trace` object and a `sort(_)` parametric object will result in `trace_0.xml` and `sort_1.xml` XML files.

Each entity XML file contains references to two other files, an XML specification file and a XSLT style-sheet file. The XML specification file can be either a DTD file (`logtalk_entity.dtd`) or an XML Scheme file (`logtalk_entity.xsd`). The XSLT 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 by the lgtdoc tool but can be overridden by passing a list of options to the tool predicates. The `lgtdoc/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 (e.g. reStructuredText, Markdown, HTML, and PDF). See the `NOTES` file in the tool directory for details. You may use the supplied sample files as a starting point for generating the documentation of your Logtalk applications.

The Logtalk DTD file, `logtalk_entity.dtd`, contains a reference to a user-customizable file, `custom.ent`, which declares XML entities for source code author names, license terms, and copyright string. After editing the `custom.ent` file to reflect your personal data, you may use the XML entities on `info/1` documenting directives. For example, assuming that the XML entities are named author, license, and copyright we may write:

    :- info([
        version is 1:1:0,
        author is {author},
        license is {license},
        copyright is {copyright}
    ]).

The entity references are replaced by the value of the corresponding XML entity when the XML documenting files are processed (not when they are generated; this notation is just a shortcut to take advantage of XML entities).

The lgtdoc tool supports a set of options that can be used to control the generation of the XML documentation files. See the tool documentation for details. There is also a doclet tool that allows automating the steps required to generate the documentation for an application.

## Inline formatting in comments text

Inline formatting in comments text can be accomplished by using Markdown or reStructuredText syntax and converting XML documenting files to Markdown or reStructuredText files (and these, if required, to e.g. HTML, ePub, or PDF formats). Note that Markdown and reStructuredText common syntax elements are enough for most API documentation:

    Mark *italic text* with one asterisk.
    Mark **bold text** with two asterisks.
    Mark ``monospaced text`` with two backquotes.

Rendering this block as markup gives:

> Mark italic text with one asterisk. Mark bold text with two asterisks. Mark `monospaced text` with two backquotes.

## Diagrams

The diagrams tool supports a wide range of diagrams that can also help in documenting an application. The generated diagrams can include URL links to both source code and API documentation. They can also be linked, connecting for example high level diagrams to detail diagrams. These features allow diagrams to be an effective solution for navigating and understanding the structure and implementation of an application. This tool uses the same reflection API as the `lgtdoc` tool and thus have access to the same source data. See the tool documentation for details.