Re: Any initial thoughts on luau?

[Hans Hagen via ntg-context <ntg-context@ntg.nl>]

On 11/5/2021 6:23 PM, Ramkumar KB via ntg-context wrote:
> Hello,
> 
> Yesterday, Roblox announced - Luau - https://luau-lang.org/why 
> <https://luau-lang.org/why> - mainly adding linting and type-checking 
> features.
> 
> Being compatible with Lua 5.1 is probably a bummer but nonetheless would 
> be interesting to hear about this from this community.
for sure i need more than an email to give a real answer (and some can 
be read between the lines of the history documents / articles that we 
ship); that said:

the main reasons for choosing lua for luatex has been that it is 
relatively small, has no dependencies, doesn't need tons of libraries to 
make it useful, is made for embeded usage, evolves in a proper academic 
setting, has long-term dedicated (nice) developers, is not part of some 
religious programming language war/competition, reminds me (in a 
positive way of pascal and modula), is pretty fast, ... so, no regrest 
and no need for something else

now, the link you point at mentions 'typing', 'multipass bytecode 
generation', 'possible jit'

to start with typing: i suppose that a more explicit integer / float 
separation can give better performance, although on modern cpu's one can 
wonder (personally i don't see the current mix of integer / float as a 
benefit over all numbers being floats  - which had some charm due to the 
consistency - but who an i to complain; at least we now have bitwise 
operators (for a specific application like roblox it makes sense but 
using a dedicated / patched / extended lua machinery in luatex doesn't); 
there are articles by the lua authors about typing but these are behind 
publisher firewalls

multipass compiling costs time and would actually not be that 
benificial: in luatex we rely a lot on instant and frequent compilation 
(\directlua, \latelua) which is real fast; i bet that there are some 
optimizations possible in the vm but at the cost of more granularity and 
therefore it could bring limitations too (unless one goes wider memory 
wise) .. i think many lua applications actually assume fast realtime 
compilation; we simply don't stay long enough in a run to have an 
advantage (apart maybe from embedded bytecode for which an optional 
bytecode optimizer could make sense and i actually have been thinking 
about that)

jitting also costs time and for a single pass process like tex there is 
no gain (we established that long ago alreadY); the only reason why 
luajittex is faster than luatex for a tex run is that the vm is faster 
due to some limitations (that one can actually hit but in context we got 
around it) ... jitting also is cpu dependent and therefore more fragile 
futurw wise (more and more complex code too)

i'd read about the roblox vm project some time ago and was curious how 
it would work with the latest lua but then, but for good reason they 
stick to 5.1; if you look at the lua vm code i guess that some gain can 
come from less type-checking (maybe the <const> prefix in 5.4 is some 
indication that there are thoughts about this but currently that has no 
significant gain)

if better performance is an objective: there are probably spots in the 
current code that are candidates and one can see from updates that 
occasionally optimizations happen (keep in mind that lua has to run on a 
wide range of hardware: small embedded to fast single core)

so, I'm pretty okay with lua as it is now (but any influx from spin off 
languages / engines can be interesting, but i think the authors are 
aware of all that) ... and ... who knows what (side effects) pallene 
will bring

(also about performance: i know pretty well how to write fast lua code 
but no one ever comes around asking so that means everyone is satisfied)

Hans

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                                           Hans Hagen | PRAGMA ADE
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