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LATEX-L  June 1998

LATEX-L June 1998

Subject:

Re: Modules

From:

Frank Mittelbach <[log in to unmask]>

Reply-To:

Mailing list for the LaTeX3 project <[log in to unmask]>

Date:

Sat, 27 Jun 1998 20:53:46 +0200

Content-Type:

text/plain

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text/plain (112 lines)

I think Richard Walker asked whether or not the Team thinks that
concepts of modules are relevant for LaTeX3.

well here are my own thoughts, Team or no Team for the moment.

i think that looking carefully at the idea of modules for structuring
code in some way is relevant for latex3 but i go with Chris who said:

 > Hans' very interesting ideas are for modules to handle the name-clash
 > problem at the document-level.
 >
 > This is certainly something that needs attention but is probably
 > independent of L3PL modularization, or maybe there is some overlap?

what he points out here with just two sentences that he thinks that
there are different levels of modularizations and essentially that a
modularization as suggested can't be used for low-level programming and
i fully agree with him here.

in other words as nice and sensible the modularizations as suggested
by Hans or in a different fashion by Volkan are (or may be) they can
probably be successfully applied in a layer that is high above the
actual programming action, eg perhaps on a document level (as
suggested by Chris) or perhaps at one level deeper in a sort of
high-level design language that is used to produce certain effects
from low-level modules which offer certain functions via such a naming
concept.

the problem then however is that this is most likely very
unsatisfactory if the same concepts can't be applied deeper down. and
my claim is they can't (at least not reasonably)

why?

a) because TeX in its current incarnations (ie TeX3, eTeX, Omega) is a
token based interpreter which works only at an acceptable speed if its
internal coding is based on tokens which can directly be looked up in
a hash table either resulting in a primitive action or into a macro
which consist of tokens. the recursion here has to be coming to an end
pretty fast and in current TeX code it reasonably does but there are a
number of recursions. if you change that to implement a manual lookup
functionality on all levels then you will find yourself slowing down
the system by i would guess a factor of 50 or more --- and even if
these days we are having bigger machines than the one i had when i
first saw LaTeX this is still far outside of what is usable.

b) a large amount of the language lives due to expansion
facilities. this is at the heart of the language like it or not and it
mainly works by altering the order of expansions on the token
level. now if you get rid of the token level and replace it my a
manual lookup mechanism then a large part of the language becomes
unusable, and there is nothing you can replace it with. if on the
other hand you make the lookup functionality usable with the expansion
paradigm then you have to slow down the process even further.

if you don't believe me i suggest you try the following medium sized
experiment:

take the plain TeX format ie plain.tex and replace all tokens \<name>
within all macro definitions by, say, !name> and at the very beginning
define something like

  \catcode`\!=\active
  \def!#1>{\csname#1\endcsname}

which would be the simplest case of name lookup. of course this is a
bit (or even more than a bit) of handwork to get this going, beside
going through all the code you would need to carefully check all the
places where the code picks up arguments as single tokens which would
now need {...}

but it might be worthwhile to try it for two reasons: a) to compare
how fast it compiles the TeX book or some comparable document
compared to compiling it with the original plain format and b) how big
the format gets compared to the original one.

b) will be drastic: a current LaTeX format (without any packages
loaded) uses about 51088 words of memory before begin document; if the
average word length in commands is 10 (which is far too low with a
consequent implemented module concept) then this gets basically blown
to 500000 which is twice the amount of main mem that i have available
on this machine for everything. i just looked: when we compiled the
Companion the log file showed 208957 words of memory out of 262141
try to imagine to what size this would grow.

so i fear this is impossible. perhaps i'm wrong and if somebody proves
me so, so much the better, but it must me something more than just the
sketch of an generic idea that makes me believe that this can work
with TeX.

for this reason our approach for LP3 was to provide a token based
language with a module concept being based on conventions rather than
absolute force. In other words \module_prog:nnn is a convention and
nobody is forced to obey it; we don't think we can enforce that (one
could make the above a variable and use it as such or define a command
with 1 argument that has this name). but we also think we don't really
need to enforce this, assuming that such (or rather a similar)
convention is finally adopted. experience with TeX code has shown that
people do obey conventions (if they get any:-): look at typical latex
code it looks like latex code, unreadable and all, with a few twists
depending on who wrote it (ie some people have their special
conventions).

of course you could surround such a language with a programming
front-end that would enforce any concept and help you along be it some
emacs more or some fancy gui support.

well, so much for my view on this. hope this is not disappointing it is
not meant to be but i think that my view is backed from years of
programming experience within TeX and in real programming languages

frank

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