GAP (GAPDoc) - Chapter 4: Distributing a Document into Several Files

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### 4. Distributing a Document into Several Files

In GAPDoc there are facilities to distribute a single document over several files. This is for example interesting, if one wants to store the documentation of some code in the same file as the code itself. Or, if one just wants to store chapters of a document in separate files. There is a set of conventions how this is done and some tools to collect the text for further processing.

#### 4.1 The Conventions

Pieces of documentation that shall be incorporated into another document are marked as follows:

    ##  <#GAPDoc Label="MyPiece">
    ##  <E>This</E> is the piece.
    ##  The hash characters are removed.
    ##  <#/GAPDoc>

This piece is then included into another file by a statement like: `<#Include Label="MyPiece">` Here are the exact rules, how pieces are gathered:

- All lines up to a line containing the character sequence "`<#GAPDoc Label="`" are ignored. The characters on the same line before this sequence are stored as "prefix". The characters after the sequence up to the next double quotes character are stored as "label". All other characters in the line are ignored.

- The following lines up to a line containing the character sequence "`<#/GAPDoc>`" are stored under the label. These lines are processed as follows: The longest possible substring from the beginning of the line that equals the corresponding substring of the prefix is removed.

Having stored a list of labels and pieces of text gathered as above this can be used as follows.

- In GAPDoc documentation files all statements of the form "`<#Include Label="Key">`" are replaced by the sequence of lines stored under the label `Key`.

- Additionally, every occurrence of a statement of the form "`<#Include SYSTEM "Filename">`" is replaced by the whole file stored under the name `Filename` in the file system.

- These substitutions are done recursively (although one should probably avoid to use this extensively).

Here is another example:

    # # <#GAPDoc Label="AnotherPiece">  some characters
    # # This text is not indented.
    #  This text is indented by one blank.
    #Not indented.
    #<#/GAPDoc>

replaces `<#Include Label="AnotherPiece">` by

    This text is not indented.
     This text is indented by one blank.
    Not indented.

Since these rules are very simple it is quite easy to write a program in almost any programming language which does this gathering of text pieces and the substitutions. In GAPDoc there is the GAP function `ComposedXMLString` (4.2-1) which does this.

Note that the XML-tag-like markup we have used here is not a legal XML markup, since the hash character is not allowed in element names. The mechanism described here is a preprocessing step which composes an XML document.

#### 4.2 A Tool for Collecting a Document

##### 4.2-1 ComposedXMLString

`> ComposedXMLString`( path, main, source ) | ( function )

Returns: XML document as string

This function returns a string containing a GAPDoc XML document constructed from several source files.

Here path must be a path to some directory (as string or directory object), main the name of a file in this directory and source a list of file names, all of these relative to path. The document is constructed via the mechanism described in Section 4.1.

First the files given in source are scanned for chunks of GAPDoc-documentation marked by `<#GAPDoc Label="...">` and `</#GAPDoc>` pairs. Then the file main is read and all `<#Include ... >`-tags are substituted recursively by other files or chunks of documentation found in the first step, respectively.

    gap> doc := ComposedXMLString("/my/dir", "manual.xml",
    > ["../lib/func.gd", "../lib/func.gi"]);;

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