Message-ID:  <9704110234.AA25815@epsilon.ams.org>
Reply-To: Mailing list for the LaTeX3 project
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In-Reply-To:  "Your message of Thu, 10 Apr 97 17:06:05 PDT." 
              <334D806D.167E@math.uci.edu>
Date:         Thu, 10 Apr 1997 22:34:16 -0400
From: Michael Downes <mjd@MATH.AMS.ORG>
Sender: Mailing list for the LaTeX3 project
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To: Multiple recipients of list LATEX-L
              <LATEX-L@RELAY.URZ.UNI-HEIDELBERG.DE>
Subject:      Re: Letterspacing (again)
Status: R

> ... it seems
> that there should be an algorithmic solution which
> extrapolates the available kerning information which
> comes very (and for some fonts maybe even indistiguishably)
> close to the optimum?  Something like a poor man's
> letterspace that's not so poor after all?

The crucial limiting factor is this: in TeX it is very difficult to
write *fully general* macros that pick up tokens one at a time and test
them before execution. Your intuition has some merit, if you are willing
that the letterspaced text should be subject to some strong
restrictions: no { } characters, no accent commands, no conditional
commands (\if... \else \fi), no macros that take arguments (such as
\ref, \index, \cite, or further font changes ...).

Then

(a) If you are willing to accept those restrictions, suitable macros can
be written without a great deal of work. But who will want to actually
use the macros then? I would certainly not use them in a documentclass
or package because they would be nothing but a minefield, waiting to
explode with mysterious error messages in the face of any user who
inadvertently uses one of the forbidden elements.

(b) For each class of problem element, it is generally possible to make
the macros handle that class, but only by multiplying the complexity and
macro-writing time tenfold for each class, and dividing the runtime
speed by ten, too. (OK, that might be an over-exaggeration, but not by
much---and it will seem even less if you are the macro writer actually
facing such a task :-) It doesn't do much good to handle two classes
and leave two others unhandled: then the macros are still a minefield
for unwary users, only the error messages turn up less often (e.g., Joe
User spent 900 hours writing his thesis without any error messages and
then the night before it's due he happens to add an accent command in a
section title which happens to be subjected to letter-spacing by the
documentclass. Surprise!).

Michael Downes, mjd@ams.org