Hello, Yesterday, Roblox announced - Luau - 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. Thank you. best regards, Ramkumar
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 ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl -----------------------------------------------------------------
On Fri Nov 5, 2021 at 9:14 PM CET, Hans Hagen via ntg-context wrote:
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
[...]
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
[...]
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)
[...]
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
After Ramkumar's initial e-mail, I reread some of the manuals describing Lua 5.1 / 5. 2 / 5.3 / 5.4 / LuaJIT evolution and evaluation. As I learned more about Lua and LuaTeX I realized that they share (or contrast in) some core concepts (e.g. TeX's hash table vs Lua tables, LuaTeX's sparse arrays vs Lua tables, custom allocation strategies - huge mem array and custom management vs garbage collection). Recently I discovered some of the things LuaJIT does (and it is in many ways incredible piece of software). So the idea of implementing LuaTeX in LuaJIT struck me. The reason why LuaJIT doesn't bring that many benefits for LuaTeX specifically (apart from the faster interpeter, is that LuaTeX heavily uses Lua C API (which is AFAIK slow in LuaJIT since it can't (couldn't?)be JIT compiled and there is the overhead of the API itself - the stack nature). Wile FFI in LuaJIT is fast. And I don't necessarilly mean calling external C functions via FFI, just defining the structures (in C syntax) and using them transparently in LuaJIT (like "specialized and fast tables"). I wonder how possible and usable would a LuaTeX implementation in pure (LuaJIT specific) Lua code would be, if it tried to offer the same API as currently described in the LuaTeX manual (hence being compatible). I can see benefits in it being pure Lua (although with some optimized structures), most of the interesting things already happen in Lua and this would just extend the approachability and openness of the engine. Also the possibilities of having garbage collection (no need to worry about memory safety), JIT being viable (since there is no use of C API to prevent it), less platform dependence (AFAIK in some cases where PUC Lua uses the platform C's functions LuaJIT provides portable alternatives). There are also arguments against LuaJIT: - weird 5.1 / 5.2 mix (probably a matter of preference) - no integer types (but actually LuaJIT internally optimizes integers and also provides the bit library, but the surface is "clean double only") - requires certain unidiomatic coding style for achieving performance - limited platform support (LuaJIT has to specifically be ported to each architecture, but the current support is pretty solid) - in the past total size of objects was limited to be 2 GiB (this is no longer true with GC64 mode) - LuaTeX specifically has had problems with LuaJIT's hash function, I don't know the details though - while the code without C API use would be JITable, the benefits may not be large, since TeX runs are not that long, although there are critical parts of code that would certainly benefit Surely I somewhere forgot an important point for or against the theoretical idea. But Hans, I would still appreciate your general opinion, even though I remember some document saying that you already disregarded this possibility. Kind regards, Michal Vlasák
On 11/6/2021 5:19 PM, Michal Vlasák wrote:
On Fri Nov 5, 2021 at 9:14 PM CET, Hans Hagen via ntg-context wrote:
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
[...]
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
[...]
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)
[...]
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
After Ramkumar's initial e-mail, I reread some of the manuals describing Lua 5.1 / 5. 2 / 5.3 / 5.4 / LuaJIT evolution and evaluation.
As I learned more about Lua and LuaTeX I realized that they share (or contrast in) some core concepts (e.g. TeX's hash table vs Lua tables, LuaTeX's sparse arrays vs Lua tables, custom allocation strategies - huge mem array and custom management vs garbage collection).
Recently I discovered some of the things LuaJIT does (and it is in many ways incredible piece of software).
So the idea of implementing LuaTeX in LuaJIT struck me. The reason why LuaJIT doesn't bring that many benefits for LuaTeX specifically (apart from the faster interpeter, is that LuaTeX heavily uses Lua C API (which is AFAIK slow in LuaJIT since it can't (couldn't?)be JIT compiled and there is the overhead of the API itself - the stack nature). Wile FFI in LuaJIT is fast. And I don't necessarilly mean calling external C functions via FFI, just defining the structures (in C syntax) and using them transparently in LuaJIT (like "specialized and fast tables").
sure, it's a nice piece of software
I wonder how possible and usable would a LuaTeX implementation in pure (LuaJIT specific) Lua code would be, if it tried to offer the same API as currently described in the LuaTeX manual (hence being compatible).
personally i would never gamble on that, just as i never gambled on luajittex for the long run ... it's nice to have around as long as it works but just as the ffilib used in luatex is 'abandoned by where it came from', luajit is also stuck in 5.2 and there was even a moment that it looked like being quit ... for me, anything that depends on low level cpu specific code at compile time is not worth the effort (it's also why i discarded libs in luametatex that have cpu specific optimizations that then in turn demand running scripts to generate files for compilation ... all not worth the trouble) now, keep in mind that (lua)jit involves some runtime analysis and that is why we don't gain (we did quite some experiments at that time) also, often the runtime is not where one thinks (many jit performance tests are doing math and we hardly do that); also in luatex we had to patch the string hasher that came with luahit because it was tuned for urls (think of skipping the first n chars i.e. http://) while for tex that actually works out bad for the record: i have rewritten bits of core tex in lua but in the end didn't see many benefits (i'll probably pick up that thread when luametatex is kind of finished) .. i need to update it -)
I can see benefits in it being pure Lua (although with some optimized structures), most of the interesting things already happen in Lua and this would just extend the approachability and openness of the engine.
as i mentioned, i will pick up that thread but still it will be via callbacks ... much in tex is about macro handling (efficient in c) and par building (efficient in c) ... crossing the c boundary is not that costly in the end (one can sort of measure that) ... it's the cpu cache (hits and misses) that matter more as lua and tex are jumping around memory (not crunching numbers or massaging vectors) ... some gain will come from the upcoming GB level 2 caches for cpu's (i guess)
Also the possibilities of having garbage collection (no need to worry about memory safety), JIT being viable (since there is no use of C API to prevent it), less platform dependence (AFAIK in some cases where PUC Lua uses the platform C's functions LuaJIT provides portable alternatives).
jit is cpu dependent
There are also arguments against LuaJIT: - weird 5.1 / 5.2 mix (probably a matter of preference)
and politics (one can find not so nice discussions on the web, one reason for not using luajit btw)
- no integer types (but actually LuaJIT internally optimizes integers and also provides the bit library, but the surface is "clean double only")
- requires certain unidiomatic coding style for achieving performance
indeed, and this while ffi mix is kind of not-so-lua i get the feeling that it also stimulates inefficient code writing .. the 'jit will do it for me' thing
- limited platform support (LuaJIT has to specifically be ported to each architecture, but the current support is pretty solid)
- in the past total size of objects was limited to be 2 GiB (this is no longer true with GC64 mode)
also some limitations on what goes on the stack
- LuaTeX specifically has had problems with LuaJIT's hash function, I don't know the details though
- while the code without C API use would be JITable, the benefits may not be large, since TeX runs are not that long, although there are critical parts of code that would certainly benefit
an alternative could be the compilation of (stable) lua code into modules (the lua folks have articles about that, and it seems to outperform luajit)
Surely I somewhere forgot an important point for or against the theoretical idea. But Hans, I would still appreciate your general opinion, even though I remember some document saying that you already disregarded this possibility.
one important point is that 'tex is also something knuthian' ... software legacy ... nice to keep it around, running and up to date we can pick up that thread in a year or so (or at a meeting) Hans ps. about performance: it's not the core engine that is the bottleneck, it's often suboptimal user styling and macro writing ... i'm often really surprised how fast lua is, and when it's taking time it's often for a reason (and yes, i spend a lot of time on benchmarking and considering optimizations without messing up code, kind of fun thing) ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl -----------------------------------------------------------------
Hans / Michal, Fascinating exchange of thoughts. Thank you so much for sharing. On the back of my mind, probably a bittersweet moment by Roblox - having built its foundations with Lua and deciding to fork / rewrite it... best regards, Ramkumar On Sun, Nov 7, 2021 at 2:39 AM Hans Hagen via ntg-context < ntg-context@ntg.nl> wrote:
On 11/6/2021 5:19 PM, Michal Vlasák wrote:
On Fri Nov 5, 2021 at 9:14 PM CET, Hans Hagen via ntg-context wrote:
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
[...]
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
[...]
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)
[...]
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
After Ramkumar's initial e-mail, I reread some of the manuals describing Lua 5.1 / 5. 2 / 5.3 / 5.4 / LuaJIT evolution and evaluation.
As I learned more about Lua and LuaTeX I realized that they share (or contrast in) some core concepts (e.g. TeX's hash table vs Lua tables, LuaTeX's sparse arrays vs Lua tables, custom allocation strategies - huge mem array and custom management vs garbage collection).
Recently I discovered some of the things LuaJIT does (and it is in many ways incredible piece of software).
So the idea of implementing LuaTeX in LuaJIT struck me. The reason why LuaJIT doesn't bring that many benefits for LuaTeX specifically (apart from the faster interpeter, is that LuaTeX heavily uses Lua C API (which is AFAIK slow in LuaJIT since it can't (couldn't?)be JIT compiled and there is the overhead of the API itself - the stack nature). Wile FFI in LuaJIT is fast. And I don't necessarilly mean calling external C functions via FFI, just defining the structures (in C syntax) and using them transparently in LuaJIT (like "specialized and fast tables").
sure, it's a nice piece of software
I wonder how possible and usable would a LuaTeX implementation in pure (LuaJIT specific) Lua code would be, if it tried to offer the same API as currently described in the LuaTeX manual (hence being compatible).
personally i would never gamble on that, just as i never gambled on luajittex for the long run ... it's nice to have around as long as it works but just as the ffilib used in luatex is 'abandoned by where it came from', luajit is also stuck in 5.2 and there was even a moment that it looked like being quit ... for me, anything that depends on low level cpu specific code at compile time is not worth the effort (it's also why i discarded libs in luametatex that have cpu specific optimizations that then in turn demand running scripts to generate files for compilation ... all not worth the trouble)
now, keep in mind that (lua)jit involves some runtime analysis and that is why we don't gain (we did quite some experiments at that time)
also, often the runtime is not where one thinks (many jit performance tests are doing math and we hardly do that); also in luatex we had to patch the string hasher that came with luahit because it was tuned for urls (think of skipping the first n chars i.e. http://) while for tex that actually works out bad
for the record: i have rewritten bits of core tex in lua but in the end didn't see many benefits (i'll probably pick up that thread when luametatex is kind of finished) .. i need to update it -)
I can see benefits in it being pure Lua (although with some optimized structures), most of the interesting things already happen in Lua and this would just extend the approachability and openness of the engine.
as i mentioned, i will pick up that thread but still it will be via callbacks ... much in tex is about macro handling (efficient in c) and par building (efficient in c) ... crossing the c boundary is not that costly in the end (one can sort of measure that) ... it's the cpu cache (hits and misses) that matter more as lua and tex are jumping around memory (not crunching numbers or massaging vectors) ... some gain will come from the upcoming GB level 2 caches for cpu's (i guess)
Also the possibilities of having garbage collection (no need to worry about memory safety), JIT being viable (since there is no use of C API to prevent it), less platform dependence (AFAIK in some cases where PUC Lua uses the platform C's functions LuaJIT provides portable alternatives).
jit is cpu dependent
There are also arguments against LuaJIT: - weird 5.1 / 5.2 mix (probably a matter of preference)
and politics (one can find not so nice discussions on the web, one reason for not using luajit btw)
- no integer types (but actually LuaJIT internally optimizes integers and also provides the bit library, but the surface is "clean double only")
- requires certain unidiomatic coding style for achieving performance
indeed, and this while ffi mix is kind of not-so-lua
i get the feeling that it also stimulates inefficient code writing .. the 'jit will do it for me' thing
- limited platform support (LuaJIT has to specifically be ported to each architecture, but the current support is pretty solid)
- in the past total size of objects was limited to be 2 GiB (this is no longer true with GC64 mode)
also some limitations on what goes on the stack
- LuaTeX specifically has had problems with LuaJIT's hash function, I don't know the details though
- while the code without C API use would be JITable, the benefits may not be large, since TeX runs are not that long, although there are critical parts of code that would certainly benefit
an alternative could be the compilation of (stable) lua code into modules (the lua folks have articles about that, and it seems to outperform luajit)
Surely I somewhere forgot an important point for or against the theoretical idea. But Hans, I would still appreciate your general opinion, even though I remember some document saying that you already disregarded this possibility.
one important point is that 'tex is also something knuthian' ... software legacy ... nice to keep it around, running and up to date
we can pick up that thread in a year or so (or at a meeting)
Hans
ps. about performance: it's not the core engine that is the bottleneck, it's often suboptimal user styling and macro writing ... i'm often really surprised how fast lua is, and when it's taking time it's often for a reason (and yes, i spend a lot of time on benchmarking and considering optimizations without messing up code, kind of fun thing)
----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl -----------------------------------------------------------------
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participants (3)
-
Hans Hagen -
Michal Vlasák -
Ramkumar KB