[NTG-context] Snooping around in LMTX: Questions about Lua global variables

Hans Hagen j.hagen at xs4all.nl
Tue Dec 22 19:06:31 CET 2020

On 12/22/2020 6:36 PM, Neven Sajko wrote:
> Hello again,
> While learning about how to drive TeX through Lua, I decided to
> recursively list all Lua global variables (actually this is traversing
> the _G table) in the LMTX environment, half to learn more Lua, half
> for getting to know ConTeXt better.
> I was quite surprised by the huge size of the environment, a file that
> contains the listing of all the globals is 42 MB long! I wonder if it
> would be possible to reduce the exposed globals by replacing some of
> them by getter and setter-like functions? That seems like it would be

not sure what you refer to but even then you need to 'get' and 'set them 
someplace which then involves tables ... it's just a large system and 
that won't change

also, when you run such tests, don't include the characters.* tables as 
most is data, and of you do it from a tex run you also see fonts and 
their data (which then means shared tables too)

> much nicer and less error prone - because Lua is so dynamic, polluting
> the global namespace seems even more dangerous than in C-like
> languages. I guess it could also be more performant, because Lua would
> conceivably spend less time managing huge tables.

Wait, you traverse global tablers so their entries are *not* global.


     context.starttabulate { "|T|T|" }
     for k, v in table.sortedhash(_G) do
         context.NC() context(type(v)) context.NC() context(k) 
context.NC() context.NR()


These are global. Many come from lua itself, then there are libraries 
than come with luametatex. The rest is context specific and again some 
are just helper modules. I notices some 6 stray locals that I fixed.

> There were also some global variables with suspicious random variation
> in values between runs of ConTeXt: I ran my Lua script like so
> multiple times (attached, in case someone is interested in it):
>      context s.lua
>      rm s.tuc s.pdf s.log
> And I found that the values of some variables unpredictably and randomly vary:

Maybe weak tables?

> The variable resolvers.suffixmap.lua sometimes has the value
> "scripts", and sometimes "lua". I think this means that files with the
> file name suffix ".lua" are sometimes classified as general scripts
> and sometimes as Lua scripts. This seems like it could even be a bug?

could be but probably more a side effect ... part of that resolver stuff 
is there for usage in tds and could be simplified in the meantime .. if 
there are hashes they can differ per document

> The variables storage.tofmodules and storage.toftables are also
> interesting: they vary from run to run like this:
> tofmodules: 0.175483 0.149536 0.150493 0.150005
> toftables: 0.008407 0.008118 0.008395 0.008116
> I'd like to know what is their purpose, if it's not to involved to explain?
timers, so indeed they can differ per run


                                           Hans Hagen | PRAGMA ADE
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