I love the concept -- I've often wished that lean languages like Lua had more support for static typing, especially given the potential performance benefits.
I also love the focus on performance. I'm curious if you've considered using a tail call design for the interpreter. I've found this to be the best way to get good code out of the compiler: https://blog.reverberate.org/2021/04/21/musttail-efficient-i... Unfortunately it's not portable to MSVC.
In that article I show that this technique was able to match Mike Pall's hand-coded assembly for one example he gave of LuaJIT's interpreter. Mike later linked to the article as a new take for how to optimize interpreters: https://github.com/LuaJIT/LuaJIT/issues/716#issuecomment-854...
You may be interested in Luau, which is the gradually-typed dialect of Lua maintained by Roblox. The game Alan Wake 2 also used it for level scripting.
I did experiment with a few different dispatch methods before settling on the one in Bolt now, though not with tailcalls specifically. The approach I landed on was largely chosen cause it in my testing competes with computed goto solutions while also compiling on msvc, but I'm absolutely open to try other things out.
From my research into the subject the easiest way to implement it would be a 'musttail' macro which falls back to a trampoline for compilers which don't support it. The problem then becomes having the function call overhead (assuming the compiler can't figure out what's going on and do tail-call optimizations anyway) on the unsupported systems with each and every opcode which is probably slower than just a Big Old Switch -- which, apparently, modern compilers are pretty good at optimizing.
The VM I've been poking at is I/O bound so the difference (probably) isn't even measurable over the overhead of reading a file. I went with a pure 'musttail' implementation but didn't do any sort of performance measurements so who knows if it's better or not.
I like 99% of this, and the thing I don't like is in the very first line of the example:
> import abs, epsilon from math
IMHO it's wrong to put the imported symbols first, because the same symbol could come from two different libraries and mean different things. So the library name is pretty important, and putting it last (and burying it after a potentially long list of imported symbols) just feels wrong.
I get that it has a more natural-language vibe this way, but put there's a really good reason that most of the languages I know that put the package/module name first:
import packageName.member; // java
from package import symbol; # python
use Module 'symbol'; # perl
Oooh, bikeshedding! To me your `import math with x as y` reads like "import all of math, making all of its symbols visible, just renaming some of them". That's different from the intended "from math, import only x (maybe with a renaming)".
FYI "the embedded scene" is likely to be interpreted as "embedded systems" rather than "embedded interpreters" even by people who know about embedded interpreters, especially since all the languages you give as an example have been attempted for use on those targets (micropython, lua, and even typescript)
True. I misread it as being for embedded, especially with the term "real-time" in the mix. Then later when there was no ARM or RISC-V support I became very confused.
I was quite excited by the description and then I noted that Bolt heavily relies on double floating point numbers. I am quite disappointed because this doesn't allow me to use Bolt in my context: embedded systems where floating point numbers are rarely supported... So I realized that I misinterpreted `embedded`.
Outperforming languages in its class is doing some heavy lifting here. Missing comparison to wasm interpreter, any of the java or dot net interpreters, the MLs, any lisps etc.
Compile to register bytecode is legitimate as a strategy but its not the fast one, as the author knows, so probably shouldn't be branding the language as fast at this point.
It might be a fast language. Hard to tell from a superficial look, depends on how the type system, alias analysis and concurrency models interact. It's not a fast implementation at this point.
> This means functions do not need to dynamically capture their imports, avoiding closure invocations, and are able to linearly address them in the import array instead of making some kind of environment lookup.
That is suspect, could be burning function identifiers into the bytecode directly, not emitting lookups in a table.
Likewise the switch on the end of each instruction is probably the wrong thing, take a look at a function per op, forced tailcalls, with the interpreter state in the argument registers of the machine function call. There's some good notes on that from some wasm interpreters, and some context on why from luajit if you go looking.
The class is "embeddable interpreted scripting language", which is not quite the same thing as just an interpreter.
Embedded interpreters are that designed to be embedded into a c/c++ program (often a game) as a scripting language. They typically have as few dependencies as possible, try to be lightweight and focus on making it really easy to interopt between contexts.
The comparison hits many of the major languages for this usecase. Though it probably should have included mono's interpreter mode, even if nobody really uses it since mono got AoT
This looks so familiar that it got me thinking: who is collating all of the languages that are being invented? I must see two dozen a year on HN. I'm not dissing OP, but I've seen so many languages I'm not sure if I'm having deja vu, or vuja de.
Really impressive, great job! I was interested to see how you had solved Result type and that seems quite developer-friendly—no wrappers just value & error union. I should try it out to see how it's to write if I can run it on ARM64. I wish Godot Script looked like this.
If functions don't have a return signature, does that mean everything must be satisfied in the compilation step?
What about memory management/ownership? This would imply that everything must be copy by value in each function callsite, right? How to use references/pointers? Are they supported?
I like the matchers which look similar to Rust, but I dislike the error handling because it is neither implicit, and neither explicit, and therefore will be painful to debug in larger codebases I'd imagine.
Do you know about Koka? I don't like its syntax choices much but I think that an effect based error type system might integrate nicely with your design choices, especially with matchers as consumers.
I see your benchmarks compare against other interpreted languages "in its class".
We read here a couple days ago about Q which is compiled. Bolt claims to "plow through code at over 500kloc/thread/second". Q claims to compile in milliseconds--so fast that you can treat it like a script.
Bolt and Q are both newborns. Perhaps you could include each other in your benchmarks to give each other a little publicity.
I might be missing this, but I'm not seeing anything about how the type system handles (or doesn't) polymorphism - generics, traits, that sort of thing. Is that in there?
Really cool! Roughly how much memory does it take to include it in an engine? Also I'm really interested in the process of creating these really fast scripting languages, have you written anything about how you wrote Bolt?
Bolt's memory usage in most cases hovers right around Lua 5.4/Luau in my own testing, but maybe I should include a few memory benchmarks to highlight that more. It does notably have a higher memory overhead during compilation than other languages in this class though.
As for writeups, I'm working on putting out some material about the creation of Bolt and my learnings now that it's out there.
Seems to be the worst of both worlds: mutable by default, and one must add a "const" keyword to the "let", disincentivizing const behavior by making it super verbose (e.g. the "final" problem from Java)
This looks awesome. Would you have any data on the performance of large number of invocations of small scripts? I am wondering at startup overhead for every script run. which the 500kloc/s may not capture well.
It depends on your exact usecase, I'm not 100% sure what you're asking. There is some overhead for invoking the compiler on a per-script basis. If you're parsing once but running a script many times, Bolt provides some tools (like reusing a preallocated thread object) to ammortize that cost
We have a server which uses Lua based script plugins. They are usually a few hundred to a few thousand lines and get invoked via APIs. I was trying to figure out how Bolt will behave in such a context and whether we could replace the Lua based plugin engine with this.
This is really cool but it's not portable to MacOs or aarm64 yet, and that kind of portability unfortunately is what appeals to me about an embeddable scripting language.
The only way to have any idea of how long a language might be still around is to look at how long it's been already around. From this perspective , you can only use older languages. The benchmarks show that Lua (and the Luau and Lua+JIT variants) is actually very competitive, so I'd stick with one of those.
In the end, weight is a kind of strength, and popularity is a kind of quality. It looks promising but you can't expect long-term support until there's more contributors and users
At this point it is too early to know. Even JavaScript took like 20 years to catch on
As of right now no - my primary target when developing this was realtime and games in particular since that's what I know best, but if there's a real target in embedded that's certainly something that could be explored.
Function return type inference is funny but I don't think it's that great of a feature. It makes it harder for a library's consumer to know how to properly use a function, and it also makes it harder for the maintainer to not break backwards compatibility inadvertently. Anyway, I'm all for experimenting.
There's nothing stopping a library author from explicitly annotating return types wherever a stable interface is important, the idea is more for smaller functions or callbacks to make use of this. Perhaps I'll make the examples clearer to reflect the intention.
Perhaps it makes more sense to say that exported function interfaces be explicit. That forces you to document the api and more carefully consider changes.
It’s great in TypeScript. In TypeScript your source can have inferred types returned, and then use a build step to produce resolved typings files (.d.ts) for distribution that have the fully specified type.
I love the concept -- I've often wished that lean languages like Lua had more support for static typing, especially given the potential performance benefits.
I also love the focus on performance. I'm curious if you've considered using a tail call design for the interpreter. I've found this to be the best way to get good code out of the compiler: https://blog.reverberate.org/2021/04/21/musttail-efficient-i... Unfortunately it's not portable to MSVC.
In that article I show that this technique was able to match Mike Pall's hand-coded assembly for one example he gave of LuaJIT's interpreter. Mike later linked to the article as a new take for how to optimize interpreters: https://github.com/LuaJIT/LuaJIT/issues/716#issuecomment-854...
Python 3.14 also added support for this style of interpreter dispatch and got a modest performance win from it: https://blog.reverberate.org/2025/02/10/tail-call-updates.ht...
You may be interested in Luau, which is the gradually-typed dialect of Lua maintained by Roblox. The game Alan Wake 2 also used it for level scripting.
I did experiment with a few different dispatch methods before settling on the one in Bolt now, though not with tailcalls specifically. The approach I landed on was largely chosen cause it in my testing competes with computed goto solutions while also compiling on msvc, but I'm absolutely open to try other things out.
Take look at the Nostradamus Distributor:
http://www.emulators.com/docs/nx25_nostradamus.htm
From my research into the subject the easiest way to implement it would be a 'musttail' macro which falls back to a trampoline for compilers which don't support it. The problem then becomes having the function call overhead (assuming the compiler can't figure out what's going on and do tail-call optimizations anyway) on the unsupported systems with each and every opcode which is probably slower than just a Big Old Switch -- which, apparently, modern compilers are pretty good at optimizing.
The VM I've been poking at is I/O bound so the difference (probably) isn't even measurable over the overhead of reading a file. I went with a pure 'musttail' implementation but didn't do any sort of performance measurements so who knows if it's better or not.
I see lua, do you know terralang?
I like 99% of this, and the thing I don't like is in the very first line of the example:
> import abs, epsilon from math
IMHO it's wrong to put the imported symbols first, because the same symbol could come from two different libraries and mean different things. So the library name is pretty important, and putting it last (and burying it after a potentially long list of imported symbols) just feels wrong.
I get that it has a more natural-language vibe this way, but put there's a really good reason that most of the languages I know that put the package/module name first:
With Typescript being the notable exception:Also autocomplete.
Though I almost never manually type out imports manually anymore.
I really like the way Elm does it, from "wide" (package) to "narrow" (symbol). I suspect this also helps language server implementation.
See https://guide.elm-lang.org/webapps/modules (scroll down to "Using Modules") for examples
Do you think approaching the way typescript does it for Bolt is a reasonable compromise here? Bolt already supports full-module renames like
So supporting something along the lines of Would be farily simple to accomplish.Or: `import math with abs as absolute, sqrt as square_root`
Oooh, bikeshedding! To me your `import math with x as y` reads like "import all of math, making all of its symbols visible, just renaming some of them". That's different from the intended "from math, import only x (maybe with a renaming)".
According to the Programming Guide, it supports aliases for imports
"In case of conflict or convenience, you can give modules an alias as well."
can't the compiler process it in reverse?
FYI "the embedded scene" is likely to be interpreted as "embedded systems" rather than "embedded interpreters" even by people who know about embedded interpreters, especially since all the languages you give as an example have been attempted for use on those targets (micropython, lua, and even typescript)
True. I misread it as being for embedded, especially with the term "real-time" in the mix. Then later when there was no ARM or RISC-V support I became very confused.
That's a good point, thank you. I've made a small edit to clarify.
I was quite excited by the description and then I noted that Bolt heavily relies on double floating point numbers. I am quite disappointed because this doesn't allow me to use Bolt in my context: embedded systems where floating point numbers are rarely supported... So I realized that I misinterpreted `embedded`.
Same here! It's very cool but my ideal use case would be on a limited ISA architecture like ESP32.
Run some examples, and it looks like this "High-performance, real-time optimized, super-fast" language is
[delayed]
Where do you get these numbers from? Looking at https://github.com/Beariish/bolt/blob/main/doc/Bolt%20Perfor... doesn’t seem to support these numbers.
Not bad for version 0.1.0. lua(jit) is no slowpoke and has had decades of performance improvements.
Outperforming languages in its class is doing some heavy lifting here. Missing comparison to wasm interpreter, any of the java or dot net interpreters, the MLs, any lisps etc.
Compile to register bytecode is legitimate as a strategy but its not the fast one, as the author knows, so probably shouldn't be branding the language as fast at this point.
It might be a fast language. Hard to tell from a superficial look, depends on how the type system, alias analysis and concurrency models interact. It's not a fast implementation at this point.
> This means functions do not need to dynamically capture their imports, avoiding closure invocations, and are able to linearly address them in the import array instead of making some kind of environment lookup.
That is suspect, could be burning function identifiers into the bytecode directly, not emitting lookups in a table.
Likewise the switch on the end of each instruction is probably the wrong thing, take a look at a function per op, forced tailcalls, with the interpreter state in the argument registers of the machine function call. There's some good notes on that from some wasm interpreters, and some context on why from luajit if you go looking.
The class is "embeddable interpreted scripting language", which is not quite the same thing as just an interpreter.
Embedded interpreters are that designed to be embedded into a c/c++ program (often a game) as a scripting language. They typically have as few dependencies as possible, try to be lightweight and focus on making it really easy to interopt between contexts.
The comparison hits many of the major languages for this usecase. Though it probably should have included mono's interpreter mode, even if nobody really uses it since mono got AoT
This looks so familiar that it got me thinking: who is collating all of the languages that are being invented? I must see two dozen a year on HN. I'm not dissing OP, but I've seen so many languages I'm not sure if I'm having deja vu, or vuja de.
Really impressive, great job! I was interested to see how you had solved Result type and that seems quite developer-friendly—no wrappers just value & error union. I should try it out to see how it's to write if I can run it on ARM64. I wish Godot Script looked like this.
If functions don't have a return signature, does that mean everything must be satisfied in the compilation step?
What about memory management/ownership? This would imply that everything must be copy by value in each function callsite, right? How to use references/pointers? Are they supported?
I like the matchers which look similar to Rust, but I dislike the error handling because it is neither implicit, and neither explicit, and therefore will be painful to debug in larger codebases I'd imagine.
Do you know about Koka? I don't like its syntax choices much but I think that an effect based error type system might integrate nicely with your design choices, especially with matchers as consumers.
[1] https://koka-lang.github.io/koka/doc/index.html
> If functions don't have a return signature, does that mean everything must be satisfied in the compilation step?
Functions do have a return signature.
It looks like the author chose to show off the feature of return type inference in the short example README code, rather than the explicit case.
https://github.com/Beariish/bolt/blob/main/doc/Bolt%20Progra...
Oh, not OP, but I love Koka. I should play around with it again thanks for reminding me!
Wow a fast scripting language with normal syntax and type checking.. Really hope this can take off and be a valid Lua alternative.
I see your benchmarks compare against other interpreted languages "in its class".
We read here a couple days ago about Q which is compiled. Bolt claims to "plow through code at over 500kloc/thread/second". Q claims to compile in milliseconds--so fast that you can treat it like a script.
Bolt and Q are both newborns. Perhaps you could include each other in your benchmarks to give each other a little publicity.
Looks cool, but please can we stop naming things ”bolt”
Yeah this is the third programming language named Bolt that I'm aware of
Not to mention the facebook after compilation optimizer called bolt.
Looks nice! Is there any plans on a language server and formatting tooling?
Usually I feel like that's bare minimum before I'd like to try and play around with a language
I might be missing this, but I'm not seeing anything about how the type system handles (or doesn't) polymorphism - generics, traits, that sort of thing. Is that in there?
Looks great, I'm especially a fan of the more C and Python syntax. Lua works, but its syntax has always been bugging me.
On the feature side, is there any support for breakpoints or a debugging server, and if not is it planned?
There's nothing like that right now, but it's absolutely something I want to explore in the future.
Really cool! Roughly how much memory does it take to include it in an engine? Also I'm really interested in the process of creating these really fast scripting languages, have you written anything about how you wrote Bolt?
Bolt's memory usage in most cases hovers right around Lua 5.4/Luau in my own testing, but maybe I should include a few memory benchmarks to highlight that more. It does notably have a higher memory overhead during compilation than other languages in this class though.
As for writeups, I'm working on putting out some material about the creation of Bolt and my learnings now that it's out there.
Congrats! I think this could be quite useful for me.
I noticed that `let`-declared variables seem to be mutable. I'd strongly recommend against that. Add a `var` keyword.
Seems to be the worst of both worlds: mutable by default, and one must add a "const" keyword to the "let", disincentivizing const behavior by making it super verbose (e.g. the "final" problem from Java)
https://github.com/Beariish/bolt/blob/0.1.0/doc/Bolt%20Progr...
Nice language! I am wondering how error handling / exceptions works in bolt?
Quickly scanned the programming guide - but wasn't able to find it. Did i miss a section?
As far as i can see it is simple, everything can return an Error, so you have to check the return value if it is an error.
https://github.com/Beariish/bolt/blob/main/examples/error_ha...
This looks awesome. Would you have any data on the performance of large number of invocations of small scripts? I am wondering at startup overhead for every script run. which the 500kloc/s may not capture well.
It depends on your exact usecase, I'm not 100% sure what you're asking. There is some overhead for invoking the compiler on a per-script basis. If you're parsing once but running a script many times, Bolt provides some tools (like reusing a preallocated thread object) to ammortize that cost
We have a server which uses Lua based script plugins. They are usually a few hundred to a few thousand lines and get invoked via APIs. I was trying to figure out how Bolt will behave in such a context and whether we could replace the Lua based plugin engine with this.
This is really cool but it's not portable to MacOs or aarm64 yet, and that kind of portability unfortunately is what appeals to me about an embeddable scripting language.
In terms of performance, how does it compare to compiled languages like the C it’s written in?
Nice, gives me Pawn vibes
(https://www.compuphase.com/pawn/pawn.htm)
It looks cool, I wish you luck in developing the language. I liked your language and I hope it becomes popular someday.
The question I ask myself when I see this kind of project is: how long are you willing to maintain it for?
My main concern about a new language is not performance, syntax, or features, but long term support and community.
The only way to have any idea of how long a language might be still around is to look at how long it's been already around. From this perspective , you can only use older languages. The benchmarks show that Lua (and the Luau and Lua+JIT variants) is actually very competitive, so I'd stick with one of those.
In the end, weight is a kind of strength, and popularity is a kind of quality. It looks promising but you can't expect long-term support until there's more contributors and users
At this point it is too early to know. Even JavaScript took like 20 years to catch on
Sounds very good, and I can see many use cases in embedded systems. But that probably requires 32-bit arm support. Is that planned ?
As of right now no - my primary target when developing this was realtime and games in particular since that's what I know best, but if there's a real target in embedded that's certainly something that could be explored.
Looks like I misinterpreted both embedded and real-time then.
game dev for 15+ years here, love the first example on Github this is compiled right? cannot replace lua?
Bolt is not compiled ahead of time, it's bytecode interpreted just like Lua
It's compiled in the same way that Lua is compiled. So yes, it can replace Lua.
If I was still writing games I would be alllllll over this
Function return type inference is funny but I don't think it's that great of a feature. It makes it harder for a library's consumer to know how to properly use a function, and it also makes it harder for the maintainer to not break backwards compatibility inadvertently. Anyway, I'm all for experimenting.
There's nothing stopping a library author from explicitly annotating return types wherever a stable interface is important, the idea is more for smaller functions or callbacks to make use of this. Perhaps I'll make the examples clearer to reflect the intention.
Perhaps it makes more sense to say that exported function interfaces be explicit. That forces you to document the api and more carefully consider changes.
It’s great in TypeScript. In TypeScript your source can have inferred types returned, and then use a build step to produce resolved typings files (.d.ts) for distribution that have the fully specified type.
Ah, true, now that you mention it. I feel like it's the best of both worlds, you get type inference and it gets documented automatically.
Awesome.
Is it deterministic like Lua?
Why is it not written in Rust?