Kollos and LuaJIT

[Jeffrey Kegler]

At a certain point in their investigation into Lua, a Wikipedian said
that it was a done deal, barring last-minute revelations that Lua has
some sort of a sordid past. The Kollos investigation of Lua is pretty
much at the same point. I'm not making a "final" announcement, but it
looks like Lua will be the language of Kollos's semantics.

As background -- Marpa allows full Perl callbacks, but these can be
slow, especially for trivial tasks. So many of the simpler tasks (such
as return the first child, or return all the children as a blessed
array) are performed with a very fast Marpa-internal mini-VM. This
mini-VM has 22 instructions -- it's evolving into a language. There's a
history of gradually evolved languages, and it's littered with disasters
-- JCL and vim macros come to mind. The Wikipedians found their
templating language was headed in a similar direction, and realized they
needed to stop before heading down that path. Lua was their answer.

I have a question, aimed at those G+ group readers who are Lua-versed
(if there are any). What version of Lua? There is now a LuaJIT, based
on Lua 5.1, which is widely used to rave reviews. It's apparently as
fast as Java's JIT, or faster, depending on which benchmark you use.
The implications of this for Kollos interface are, I think, obvious.

Lua's latest stable version is 5.2, but LuaJIT is based on Lua 5.1, with
selected Lua 5.2 features added. Users seem to be happy with this.

CPAN has a Alien::LuaJIT, which installs LuaJIT version 2.0.2. I'm
thinking of requiring (at least initially) LuaJIT 2.0.2 or better.

Thanks, jeffrey

[Christopher Layne]

I'm not going to lie. The prospect of Lua vs the existing C/XS implementation has me worrying in ways for the same reasons Java and JIT complexity make me worry in general (too much complexity). I do understand where you're coming from, implementation-wise of libmarpa, but quite simply, is it slower or faster than R2?

I do understand the concern of "it feels like I'm developing something here that has already been developed" - however, consider the *curve* of that development. You may have 22 ops, but do you expect a 100? Is the creation of a mini-VM a symptom rather than a solution; e.g. symptom of slow callbacks.

BTW: On a whim, I converted all of the action callbacks in one of my Marpa::R2 grammar's to be entirely XS implementations. They were simple callbacks, which you've already seen, but the overall performance difference? Less than 5-10%. I credit this to Marpa's own internal implementation carrying most of the efficiency.

Remember: is the mini-vm a symptom or a real solution for a problem?

-cl

[Jeffrey Kegler]

I'm not committed to the JIT, by any means. Lua is the what I'd have
evolved Marpa::R2 semantics into, or at least what I'd have done if I
was as smart as Roberto, and I can always fall back on Lua. They're
compatible -- the LuaJIT team is more committed to backward Lua
compatibility than Lua's own development team is. So as long as I code
to Lua 5.1, it's just a matter of linking to a different shared
library. And JIT or no JIT, Lua looks like the way to go.

-- jeffrey

[Ron Savage]

I know nothing about Lua except for watching 1 presentation, but I'd go for LuaJIT. Why? Because I don't see any risk of over-committing with that decision. If you later wish to switch to Lua 5.2, it would not be difficult, would it?

[Jeffrey Kegler]

As long as I'm in very early alpha/experimental phase, the risk is limited.  At thjs point, Kollos/R3 users should only be those who want to experiment along with me.  -- jeffrey

On 07/29/2014 08:22 PM, Ron Savage wrote:

I know nothing about Lua except for watching 1 presentation, but I'd go for LuaJIT. Why? Because I don't see any risk of over-committing with that decision. If you later wish to switch to Lua 5.2, it would not be difficult, would it?

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[Jeffrey Kegler]

@Christopher: I've thought more about this point (that is, which version
of Lua to go with) -- you're certainly right about the dangers of
chasing speed early in the decision making, and the inadvisability of
tieing Marpa into any single outside technology so large and complex as
a JIT. The chase for efficiency may not be the root of all evils, but
it certainly is the source of a lot of them.

Wikipedia recently switched their templating to Lua. They went with Lua
5.1, leaving LuaJIT as an option for the future. Lua's plain ol'
interpreter is very fast, and in Wikipedia's case it was already
delivering more benefits then they could absorb, including some major
speedups. So while the additional speedup from a JIT was certainly
desirable for the future, it was not an immediate priority at Wikipedia.

LuaJIT's team is committed to Lua 5.1 compatibility, so that Wikipedia
expects their Lua 5.1 templating code can run unchanged when (and if)
they move to LuaJIt.

Kollos/Marpa::R3 might do well to imitate the Wikipedians here and start
out on the basis of Lua 5.1.

-- jefrey

On 07/29/2014 01:09 PM, Christopher Layne wrote: