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84 Interface to the GAP Help System
84.1 Installing and Removing a Help Book
84.1-1 HELP_ADD_BOOK
84.1-2 HELP_REMOVE_BOOK
84.2 The manual.six File
84.3 The Help Book Handler
84.4 Introducing new Viewer for the Online Help
84.4-1 HELP_VIEWER_INFO

### 84 Interface to the GAP Help System

In this chapter we describe which information the help system needs about a manual book and how to tell it this information. The code which implements this interface can be found in `lib/helpbase.gi`.

If you are intending to use a documentation format that is already used by some other help book you probably don't need to know anything from this chapter. However, if you want to create a new format and make it available to GAP then hopefully you will find the necessary information here.

The basic idea of the help system is as follows: One tells GAP a directory which contains a file `manual.six`, see 84.1. When the GAP help is asked something about this book it reads in some basic information from the file `manual.six`: strings like section headers, function names, and index entries to be searched by the online help; information about the available formats of this book like text, html, dvi, and pdf; the actual files containing the documentation, corresponding section numbers, and page numbers: and so on. See 84.2 for a description of the format of the `manual.six` file.

It turns out that there is almost no restriction on the format of the `manual.six` file, except that it must provide a string, say `"myownformat"` which identifies the format of the help book. Then the basic actions on a help book are delegated by the help system to handler functions stored in a record `HELP_BOOK_HANDLER.myownformat`. See 84.3 for information which functions must be provided by the handler and what they are supposed to do. The main work to teach GAP to use a new document format is to write these handler functions and to produce an appropriate `manual.six` file.

#### 84.1 Installing and Removing a Help Book

##### 84.1-1 HELP_ADD_BOOK

`‣ HELP_ADD_BOOK`( short, long, dir ) | ( function )

This command tells GAP that in directory dir (given as either a string describing the path relative to the GAP root directory `GAPInfo.RootPaths[1]` or as directory object) contains the basic information about a help book. The string short is used as an identifying name for that book by the online help. The string long should be a short explanation of the content of the book. Both strings together should easily fit on a line, since they are displayed with `?books`.

It is possible to reinstall a book with different strings short, long; (for example, documentation of a not-loaded GAP package indicates this in the string short and if you later load the package, GAP quietly changes the string short as it reinstalls its documentation).

The only condition necessary to make the installation of a book valid is that the directory dir must contain a file `manual.six`. The next section explains how this file must look.

##### 84.1-2 HELP_REMOVE_BOOK

`‣ HELP_REMOVE_BOOK`( short ) | ( function )

This command tells GAP not to use the help book with identifying name short any more. The book can be re-installed using `HELP_ADD_BOOK` (84.1-1).

#### 84.2 The manual.six File

The first non-empty line of `manual.six` should be of the form

`#SIXFORMAT` myownformat

where myownformat is an identifying string for this format. The reading of the (remainder of the) file is then delegated to the function `HELP_BOOK_HANDLER.myownformat.ReadSix` which must exist. Thus there are no further regulations for the format of the `manual.six` file, other that what you yourself impose. If such a line is missing then it is assumed that the `manual.six` file complies with the `gapmacro.tex` documentation format, which internally is referred to as the `default` format for historical reasons. In that case reading the file is delegated to `HELP_BOOK_HANDLER.default.ReadSix`.

Section 84.3 explains how the return value of `HELP_BOOK_HANDLER.myownformat.ReadSix` should look like and which further function should be contained in `HELP_BOOK_HANDLER.myownformat`.

#### 84.3 The Help Book Handler

For each document format myownformat there must be a record `HELP_BOOK_HANDLER.myownformat` of functions with the following names and functionality.

An implementation example of such a set of handler functions is the `default` format, which is the format name used for the `gapmacro.tex` documentation format, and this is contained in the file `lib/helpdef.gi`.

The package GAPDoc (see Chapter GAPDoc: Introduction and Example) also defines a format (as it should) which is called: `GapDocGAP` (the case is significant).

As you can see by the above two examples, the name for a document format can be anything, but it should be in some way meaningful.

`ReadSix( stream )`

  For an input text stream stream to a `manual.six` file, this must return a record info which has at least the following two components: `bookname` which is the short identifying name of the help book, and `entries`. Here info`.entries` must be a list with one entry per search string (which can be a section header, function name, index entry, or whatever seems sensible to be searched for matching a help query). A match for the GAP help is a pair (info, i) where i refers to an index for the list info`.entries` and this corresponds to a certain position in the document. There is one further regulation for the format of the entries of info`.entries`. They must be lists and the first element of such a list must be a string which is printed by GAP for example when several matches are found for a query (so it should essentially be the string which is searched for the match, except that it may contain upper and lower case letters or some markup). There may be other components in info which are needed by the functions below, but their names and formats are not prescribed. The stream argument is typically generated using `InputTextFile` (10.5-1), e.g.

      gap> dirs := DirectoriesLibrary( "doc/ref" );;
      gap> file := Filename( dirs, "manual.six" );;
      gap> stream := InputTextFile( file );;

`ShowChapters( info )`

  This must return a text string or list of text lines which contains the chapter headers of the book info`.bookname`.

`ShowSection( info )`

  This must return a text string or list of text lines which contains the section (and chapter) headers of the book info`.bookname`.

`SearchMatches( info, topic, frombegin )`

  This function must return a list of indices of info`.entries` for entries which match the search string topic. If frombegin is `true` then those parts of topic which are separated by spaces should be considered as the beginnings of words to decide the matching. It frombegin is `false`, a substring search should be performed. The string topic can be assumed to be already normalized (transformed to lower case, and whitespace normalized). The function must return a list with two entries `[exact, match]` where `exact` is the list of indices for exact matches and `match` a list of indices of the remaining matches.

`MatchPrevChap( info, i )`

  This should return the match [info, `j`] which points to the beginning of the chapter containing match [info, i], respectively to the beginning of the previous chapter if [info, i] is already the beginning of a chapter. (Corresponds to `?<<`.)

`MatchNextChap( info, i )`

  Like the previous function except that it should return the match for the beginning of the next chapter. (Corresponds to `?>>`.)

`MatchPrev( info, i )`

  This should return the previous section (or appropriate portion of the document). (Corresponds to `?<`.)

`MatchNext( info, i )`

  Like the previous function except that it should return the next section (or appropriate portion of the document). (Corresponds to `?>`.)

`HelpData( info, i, type )`

  This returns for match [info, i] some data whose format depends on the string type, or `fail` if these data are not available. The values of type which currently must be handled and the corresponding result format are described in the list below.

`SubsectionNumber( info, i )`

  This returns some GAP object that identifies the position in the book where the display of this entry is started. This can be useful to detect if several help book entries actually point to the same place.

The `HELP_BOOK_HANDLER.myownformat.HelpData` function must recognize the following values of the type argument.

`"text"`

  This must return a corresponding text string in a format which can be fed into the `Pager`, see `Pager` (2.4-1).

`"url"`

  If the help book is available in HTML format this must return an URL as a string (Probably a `file://` URL containing a label for the exact start position in that file). Otherwise it returns `fail`.

`"dvi"`

  If the help book is available in dvi-format this must return a record of form `rec( file := filename, page := pagenumber )`. Otherwise it returns `fail`.

`"pdf"`

  Same as case `"dvi"`, but for the corresponding pdf-file.

`"secnr"`

  This must return a pair like `[[3,3,1], "3.3.1"]` which gives the section number as chapter number, section number, subsection number triple and a corresponding string (a chapter itself is encoded like `[[4,0,0], "4."]`). Useful for cross-referencing between help books.

#### 84.4 Introducing new Viewer for the Online Help

To introduce a new viewer for the online help, one should extend the global record `HELP_VIEWER_INFO` (84.4-1), the structure of which is explained below.

##### 84.4-1 HELP_VIEWER_INFO

`‣ HELP_VIEWER_INFO` | ( global variable )

The record `HELP_VIEWER_INFO` contains one component for each help viewer. Each such component is a record with two components: `.type` and `.show`.

The component `.type` refers to one of the `type`s recognized by the `HelpData` handler function explained in the previous section (currently one of `"text"`, `"url"`, `"dvi"`, or `"pdf"`).

The component `.show` is a function which gets as input the result of a corresponding `HelpData` handler call, if it was not `fail`. This function has to perform the actual display of the data. (E.g., by calling a function like `Pager` (2.4-1) or by starting up an external viewer program.)

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