The Example package is intended to be a prototype for a package. Here we describe just what features one should emulate when writing one's own GAP package for popular consumption, and a few pointers as to where to go for more information. Much of what is written here is amplified in the section Writing a GAP Package in the Extending GAP Manual.
This section is intended to amplify the recommendations made in Section The Files of a GAP Package of the Extending GAP Manual.
A GAP package should have an alphanumeric name (package-name, say); mixed case is fine, but there should be no whitespace. The directory package-dir containing the files of package package-name should be just package-name converted to lowercase (the restriction that package-dir must contain only lowercase characters may change in the future).
The directory package-dir should be a subdirectory of pkg and
preferably should have the following structure (below, a trailing /
distinguishes directories from ordinary files):
package-dir/
README
configure
Makefile.in
PackageInfo.g
init.g
read.g
doc/
lib/
src/
We now describe the above files and directories:
READMEftp- and
web-sites) instructions, as well as installation instructions and names
of the package authors and their email addresses. The installation
instructions and authors' names and addresses should be repeated in the
package's documentation (which should be in the doc directory).
configure, Makefile.insrc directory).
The configure and Makefile.in files of the Example package provide
prototypes. The configure file typically takes a path path to the
GAP root directory as argument and uses the value assigned to
GAParch in the file sysinfo.gap (created when GAP was compiled) to
determine the compilation architecture, inserts this in place of the
string @GAPARCH@ in Makefile.in and creates a file Makefile. When
make is run (which, of course, reads the constructed Makefile), a
directory bin (if necessary) and a subdirectory of bin with name
equal to the string assigned to GAParch in the file sysinfo.gap
should be created; any binaries constructed by compiling the code in
src should end up in this subdirectory of bin.
PackageInfo.gPackageInfo.g file.
The Example package's PackageInfo.g file is well-commented and
should be used as a prototype.
init.g, read.ginit.g (see Section The Files of a GAP Package in the Extending GAP Manual). As of GAP 4.4, the
typical init.g and read.g files should normally consist entirely of
ReadPackage (see ReadPackage in the GAP 4 Reference Manual)
commands (and possibly also Read commands). If the ``declaration'' and
``implementation'' parts of the package are separated (and this is
recommended), there should be a read.g file. The ``declaration'' part
of a package consists of function and variable name declarations and
these go in files with .gd extensions; these files are read in via
ReadPackage commands in the init.g file. The ``implementation'' part
of a package consists of the actual definitions of the functions and
variables whose names were declared in the ``declaration'' part, and
these go in files with .gi extensions; these files are read in via
ReadPackage commands in the read.g file. The reason for following the
above dichotomy is that the read.g file is read after the init.g
file, thus enabling the possibility of a function's implementation to
refer to another function whose name is known but is not actually defined
yet. The GAP code (whether or not it is split into ``declaration'' and
``implementation'' parts) should go in the package's lib directory (see
below).
docdoc directory as a prototype, which you will observe contains
the following files:
manual.tex # master file
.tex # chapter file(s) ... 1 for each chapter
manual.mst # MakeIndex style file
make_doc # script that generates the manuals
manual.bib BibTeX database file
(or write one's own bibliography manual.bbl file). Generating the
various formats of the manuals requires various software tools which are
called directly or indirectly by make_doc and these are listed in
Section Documentation Software Tools Needed. The file manual.mst is
needed for generating a manual index; it should be a copy of the one
provided in the Example package. The only adjustments that a package
writer should need to make to make_doc is to replace occurrences of the
word Example with package-name.
lib.g, .gd and
.gi files (other than PackageInfo.g, init.g and read.g). For some
packages (the Example package included), the directory gap has been
used instead of lib; lib has the slight advantage that it is the
default subdirectory of a package directory searched for by the
DirectoriesPackageLibrary command (see DirectoriesPackageLibrary
in the GAP 4 Reference Manual).
srcsrc directory. If there are .h ``include''
files you may prefer to put these all together in a separate include
directory.
Whether you use the traditional gapmacro.tex TeX-based system or
GAPDoc you will need to have the various following TeX tools
installed:
tex (or latex for GAPDoc), bibtex and makeindex.dvi;
dvips.ps; and
pdftex or gs and ps2pdf (or pdflatex for GAPDoc).pdf;
Note that using gs and ps2pdf in lieu of pdftex or pdflatex is a
poor substitute unless your gs is at least version 6.xx for some
xx.
The rest of this section describes the various additional tools needed
for the gapmacro.tex documentation system.
To produce the .dvi, .ps and .pdf manual formats, the following
GAP tools (usually located in GAP's main doc directory) are
needed (provided by toolsXXX.zoo for some version number XXX at the
GAP ftp- or web-sites, or can be obtained by emailing
support@gap-system.org).
gapmacro.tex
manualindexawk script that adjusts the TeX-produced index entries
and calls makeindex to process them.
mrabbrev.bibmrabbrev.bib should be located in GAP's main doc directory. To
find it on your system, try:
kpsewhich mrabbrev.bib
If your manual cross-refers to other gapmacro.tex-produced manuals (and
so has \UseReferences commands in its manual.tex), then a
manual.lab file (generated by running tex manual) for each such other
manual is needed (this includes the ``main'' manuals, e.g. those in the
doc/ref, doc/ext etc. directories).
If your manual cross-refers to GAPDoc-produced manuals (and so
has \UseGapDocReferences commands in its manual.tex), then
manual.lab files need to be generated for these too. Since GAP 4.3,
this is done by starting GAP and running:
gap> GapDocManualLab( "package" );
for each package whose manual is cross-referred to.
To produce an HTML version of the manual one needs the Perl 5 program
convert.pl which is usually located in the subdirectory etc of the
GAP root directory. The etc directory is not part of the usual
GAP distribution. The etc directory files are obtained from
toolsXXX.zoo for some version number XXX at the GAP ftp- or
web-sites, or can be obtained by emailing
support@gap-system.org.
Finally, to ensure the mathematics formulae are rendered as well as they
can be in the HTML version, one should also have the program tth
(TeX to HTML converter); convert.pl calls tth to translate
mathmode formulae to HTML (if it's available). The tth program is easy
to compile and can be obtained from
http://hutchinson.belmont.ma.us/tth/tth-noncom/download.html
As a package author, you are not obliged to provide an HTML version of
your package manual, but if you have kept to the guidelines in
Section The gapmacro.tex Manual Format of the Extending GAP
Manual, you should have no trouble in producing one. A prototype of the
command to execute is in the file make_doc; note that the HTML manual
is produced in files with .htm extensions in a directory htm outside
the doc directory. The beginning of the file convert.pl contains
instructions on its usage should you need them.
In writing the GAP code for your package you need to be a little careful on just how you define your functions and variables.
Firstly, in general one should avoid defining functions and variables via assignment statements in the way you would interactively, e.g.
gap> Cubed := function(x) return x^3; end;
The reason for this is that such functions and variables are easily overwritten and what's more you are not warned about it when it happens.
To protect a function or variable against overwriting there is the
command BindGlobal (see BindGlobal in the GAP Reference
Manual), or alternatively (and equivalently) you may define a global
function via a DeclareGlobalFunction and InstallGlobalFunction pair
or a global variable via a DeclareGlobalVariable and InstallValue
pair. There are also operations and their methods, and related objects
like attributes and filters which also have Declare... and Install...
pairs.
Secondly, it's a good idea to reduce the chance of accidental
overwriting by choosing names for your functions and variables that begin
with a string that identifies it with the package, e.g. some of the
undocumented functions in the Example package begin with Eg. This is
especially important in cases where you actually want the user to be able
to change the value of a function or variable defined by your package,
for which you haved used direct assignments (for which the user will
receive no warning if she accidentally overwrites them). It's also
important for functions and variables defined via BindGlobal,
DeclareGlobalFunction/InstallGlobalFunction and
DeclareGlobalVariable/InstallValue, in order to avoid name clashes
that may occur with (extensions of) the GAP library and other
packages. On the other hand, operations and their methods (defined via
DeclareOperation, InstallMethod etc. pairs) and their relatives do
not need this consideration, as they avoid name clashes by allowing for
more than one ``method'' for the same-named object.
The method Recipe was included in the Example package to demonstrate
the definition of a function via a DeclareOperation/InstallMethod
pair; Recipe( FruitCake ); gives a ``method'' for making a fruit cake
(forgive the pun).
Thirdly, functions or variables with SetXXX or HasXXX names
(even if they are defined as operations) should be avoided as these may
clash with objects associated with attributes or properties (attributes
and properties XXX declared via the DeclareAttribute and
DeclareProperty commands have associated with them testers of form
HasXXX and setters of form SetXXX).
Fourthly, it is a good idea to have some convention for internal functions and variables (i.e. the functions and variables you don't intend for the user to use). For example, they might be entirely capitalised.
Finally, note the advantage of using
DeclareGlobalFunction/InstallGlobalFunction,
DeclareGlobalVariable/InstallValue, etc. pairs (rather than
BindGlobal) to define functions and variables, which allow the package
author to organise her function- and variable- definitions in any order
without worrying about any interdependence. The Declare... statements
should go in files with .gd extensions and be loaded by ReadPackage
statements in the package init.g file, and the Install... definitions
should go in files with .gi extensions and be loaded by ReadPackage
statements in the package read.g file; this ensures that the .gi
files are read after the .gd files. All other package code should go
in .g files (other than the init.g and read.g files themselves) and
be loaded via ReadPackage statements in the init.g file.
It is a good idea to declare an InfoClass for your package. This gives
the package user the opportunity to control the verbosity of output
and/or the possibility of receiving debugging information (see Info functions in the GAP Reference Manual). Below, we give a quick
overview of its utility.
An InfoClass is defined with a DeclareInfoClass( InfoPkgname );
statement and may be set to have an initial InfoLevel other than the
zero default (which means no Info statement is to output information)
via a SetInfoLevel( InfoPkgname, level ); statement. An initial
InfoLevel of 1 is typical.
Info statements have the form: Info( InfoPkgname, level, expr1,
expr2, ... ); where the expression list expr1, expr2, ...
appears just like it would in a Print statement. The only difference is
that the expression list is only printed (or even executed) if the
InfoLevel of InfoPkgname is at least level.
Since GAP 4.4, the package banner, if one is desired, should be
provided by assigning a string to the BannerString field of the record
argument of SetPackageInfo in the PackageInfo.g file.
It is a good idea to have a hook into your package documentation from your banner. The Example package suggests to the GAP user:
For help, type: ?Example package
In order for this to display the introduction of the Example package
an \atindex equivalent of the following index-entry:
\index{Example package}
was added just before the first paragraph of the introductory section in
the file example.tex. The Example package uses the gapmacro.tex
system (see Section Documentation Software Tools Needed) for
documentation (you will need some different scheme to achieve this using
GAPDoc).
In the past, it was recommended that your GAP package should be packed
via the zoo program, but now any of four different archive formats are
accepted (see Section Wrapping Up a GAP Package in the Extending
GAP Manual for the details). The Example package file make_zoo
provides a template packing-up script that uses zoo. The etc
directory obtained from toolsXXX.zoo for some version number XXX
(this is described above in Section Documentation Software Tools Needed) contains a file packpack which provides a more versatile
packing-up script.
You will notice that there is a file VERSION which contains the current
version of the Example package. Such a file is entirely optional. Note
that this file is not read at all when GAP loads the package. GAP
establishes the package version by reading the PackageInfo.g file. The
current maintainer of the Example package finds it convenient to have
a file VERSION that is read both by doc/manual.tex and make_zoo. It
is however important that each new version of a package has a new number
and that version numbers of successive package versions increase
(see Version Numbers in the Extending GAP Manual for the
details).
It's also useful to have a CHANGES file that records the main changes
between versions of your package.
When your package is ready to be refereed and/or made available as an ``accepted'' GAP package, it may be of benefit to obtain CVS access to GAP; as a first step towards this you should make a request to the GAP team via an email to support@gap-system.org.
Example manual