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Date: Thu, 20 Jul 1995 11:05:21 -0300 (BST)
From: David Carlisle <carlisle@CS.MAN.AC.UK>
Sender: Mailing list for the LaTeX3 project <LATEX-L@VM.URZ.UNI-HEIDELBERG.DE>
To: Multiple recipients of list LATEX-L <LATEX-L@VM.URZ.UNI-HEIDELBERG.DE>
Subject: Re: latex/1600: LaTeX2e licensing terms
Status: R

Richard Stallman just asked me to forward the following message to
latex-l. I shall put the full text of his message, followed by
some comments in reply from me after ===========================

David

===========================

From: Richard Stallman <rms@gnu.ai.mit.edu>
To: carlisle@cs.man.ac.uk
Subject: Re: latex/1600: LaTeX2e licensing terms
Date: Thu, 20 Jul 1995 02:42:40 -0400


 [Would you please forward this to latex-l, since I cannot
 send to it directly?]

 On 26 June, you sent me a message describing two ways of effectively
 customizing how LaTeX handles article.sty (see below).

 I think these two methods are adequate to permit customization and
 therefore to make LaTeX free software.  But I don't know enough to be
 completely sure.  I have a question about each one.

     Whenever it starts up, and the `initex' file is called something other
     that latex.ltx, say fsflatex.ltx then the user can be suppled with
     an option of using `latex' or `fsflatex' commands on a standard LaTeX
     document to achieve different typesetting effects.

     The fsflatex format could do whatever you wanted but in particular it
     might have redefined \documentclass so that \documentclass{article}
     loads article.fsf (if that file exists) in preference to the standard
     article.cls. Or any other modification you care to choose.

 This method seems sufficient, provided that TeX provides a way to
 check silently whether foo.fsf exists.  I don't know of one.  Is there
 one?

     So once the fsfcustom package is written, you can distribute the
     following shell script `fsflatex' (for unix but easily ported)

     #!/bin/sh
     latex "\AtBeginDocument{\usepackage{fsfcustom}} \input" $*

 This method would work, provided there is a way for fsfcustom to check
 which document class was specified, and do different things
 accordingly.  Is that easy to do?


 Here's what you sent me on 26 June:
 ======================================================================
 So one way of making a customisation is to modify the article class to
 fsfarticle. This is a reasonable way of making a `new class' but as
 you say, it is an inconvenience if the intention is to differently
 format documents that are marked up to use article class, as all such
 documenmts would need to be modified.

 However one may instead *modify the format source files* As long as
 the typeout banner is changed so that it says something like

 LaTeX2e (FSF version) 1995/06/01

 Whenever it starts up, and the `initex' file is called something other
 that latex.ltx, say fsflatex.ltx then the user can be suppled with
 an option of using `latex' or `fsflatex' commands on a standard LaTeX
 document to achieve different typesetting effects.

 The fsflatex format could do whatever you wanted but in particular it
 might have redefined \documentclass so that \documentclass{article}
 loads article.fsf (if that file exists) in preference to the standard
 article.cls. Or any other modification you care to choose.

 Actually though, I prefer a second way of providing the user with an
 `alternative LaTeX'. You may place whatever customisations you want in
 a package file, say fsfcustom.sty so that using standard LaTeX one
 would apparently need to edit

 \documentclass{article}                \documentclass{article}
 ...                                    ...
                                        \usepackage{fsfcustom}%%%%%%<<<<<
 \begin{document}            to         \begin{document}
 ...                                    ...
 \end{document}                         \end{document}

 However there is no need to edit the files, as long as the operating
 system has even the most basic scripting language, as you can use the
 fact that TeX can read from the command line.

 So once the fsfcustom package is written, you can distribute the
 following shell script `fsflatex' (for unix but easily ported)

 #!/bin/sh

 latex "\AtBeginDocument{\usepackage{fsfcustom}} \input" $*


 I use basically this technique to supply local users with a
 `pslatex' command that uses Adobe fonts on documents rather than the
 standard TeX Computer Modern fonts.

 This method of making a customised LaTeX command has the big advantage
 that a user can send her file to a user of standard LaTeX, just by
 adding the \usepackage{fsfcustom} line to the document (and sending
 the fsfcustom package along with the document file)


===========================================================================

[ back to me ...]

Richard.

Yes the two sketches that I sent were just basic examples.
As you say, in a `production' version you would probably want
conditional code depending on whether a file exists or what class was
loaded etc.

Fortunately LaTeX makes this particularly easy as it has the following
constructs

\IfFileExists{filename}{yes code}{no code}
\@ifclassloaded{class names}{yes code}{no code}

What I had in mind was that cfgguide.tex (which describes the
customisation possibilities of LaTeX) could have a final section
saying something like (expanded into grammatical English:-).

If you need to make a version of LaTeX that differs from the standard
version in ways that are not possible using the above configuration
possibilities then you may do this as long as you read modguide.tex,
respect file name changing rules in legal.txt and change relevent
typeout banners and give the modified command a name other than latex.

Followed by a couple of `worked examples' as in the above mail message.


David