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Creating Languages in Racket (acm.org)
4 points by kinnard 162 days ago | 10 comments


3 points by krapp 160 days ago | link

Would anyone recommend Racket for a toe-headed newbie who wants to learn how to implement their own language after ruining Arc for a bit? Language development is something I've wanted to do for a while but I have no background in type theory, compilers, or anything of that sort.

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3 points by shawn 157 days ago | link

No. I feel slightly bad for being so blunt, but Racket's language facilities have absorbed more of my mental time and energy than any other aspect of Racket.

Let's put it this way. Racket is an excellent choice for implementing languages. It has every feature you could want. And yet it is very difficult to do even the simplest things. For example, when an error is raised in Anarki, you'll see a stack trace that points to ac.rkt rather than the actual location within the arc file that caused the error. This is because, frankly, ... Well, let's just say I've redacted some expletives here. But those expletives were aimed at the fact that it's really quite difficult to translate the vision in your mind into an implementation using Racket.

Now, that being said, if you sit down with Racket and take the time to learn it, you will find that it's one of the most robust, flexible, and performant language runtimes in existence. The thread-local variable support is a killer feature. The custodian support is rock solid, which makes sandboxing trivial and super reliable. And it's the premiere implementation of Scheme, so it might continue to have a thriving community for decades to come. But it took me years to become very effective with Racket. (This says more about my own shortcomings than about Racket, though!)

I would suggest checking out Scott Bell's Lumen lisp: https://docs.ycombinator.lol/

It's a Lisp that runs in both JS and Lua. It's self-hosted, meaning all .js and .lua code is generated by Lumen itself. Diff this technique with the fact that ac.scm is written in Scheme rather than Arc. Very mysterious! I remember how electrifying it felt that first day I stumbled across it and realized the significance of what I was looking at.

It's one of the most incredible projects I've ever seen. It's so small and clear, yet does so much – a perfect example of why simple systems run circles around competitors.

No matter what your experience level is with Lisp, the code will seem straightforward: https://github.com/sctb/lumen/blob/55b14ca8aafeaf6b0ca1b636d...

There is a branch that adds Python support at https://github.com/shawwn/lumen/tree/features/python which speaks to Lumen's flexibility and power. (I wonder if there is another Lisp that you can use natively from three different languages without any FFI. And if there is, I doubt it's <3000 lines.)

At this point I use Lumen to explore new languages. E.g. I learned R by implementing a Lumen to R compilation target: https://github.com/sctb/lumen/pull/193

You can also do some things with Lumen that I'm not sure you can do with any other Lisp. I hesitate to claim that, but... Well. Wanna see a magic trick? https://news.ycombinator.com/item?id=17958650

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2 points by rocketnia 157 days ago | link

"[Racket] has every feature you could want. And yet it is very difficult to do even the simplest things. For example, when an error is raised in Anarki, you'll see a stack trace that points to ac.rkt rather than the actual location within the arc file that caused the error."

Is that really "the simplest things"? :-p It seems to me Arc goes out of its way to avoid interleaving source location information on s-expressions the way Racket does. Putting it back, without substantially changing the way Arc macros are written, seems to me like it would be pretty complicated, and that complication would exist whether Arc was implemented in Racket or not. (I think aw's approach is promising here.)

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It's fun to see Lumen is designed for compiling to other languages even when it's self-hosted. That's always how I figured Arc or pretty much any of my languages would have been written once they were self-hosted.

I've been trying to write Racket libraries that (among other benefits) let me implement Cene in Racket the way I'd like to implement Cene in Cene, which should make it an easier process to port it into a self-hosting Cene implementation. But I certainly don't have it working yet, the way Lumen clearly is. :)

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3 points by shawn 153 days ago | link

Is that really "the simplest things"? :-p It seems to me Arc goes out of its way to avoid interleaving source location information on s-expressions the way Racket does. Putting it back, without substantially changing the way Arc macros are written, seems to me like it would be pretty complicated, and that complication would exist whether Arc was implemented in Racket or not.

Surprisingly it's possible to get pretty close. The trick is to read-syntax rather than read, and then have ac map over syntax objects properly. At that point it's a matter of using eval-syntax rather than eval.

The takeaway is that the error messages are much, much nicer. I'm talking "the error is at line 213 of app.arc in function init-userinfo" nicer.

It's not perfect. And to get to perfect, you'd have to do as you say and rework how macros behave. But it's maybe 90% of the benefit with little work.

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2 points by akkartik 157 days ago | link

That's really cool, thanks for making the case for Lumen. I now have it on my todo list to determine how much the standard library of Lumen matches the names Arc uses.

On a slight tangent, ycombinator.lol is not affiliated with Y Combinator, and https://github.com/lumen-language is not affiliated with Scott Bell the creator of Lumen. I clarify this because it took me a while to figure out. Am I characterizing it right, Shawn?

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2 points by i4cu 155 days ago | link

> I now have it on my todo list to determine how much the standard library of Lumen matches the names Arc uses.

Lumen looks awesome. I was looking for the docs to determine how much of arc actually exists within lumen, but I couldn't find anything. So if you do this, please let me know.

Also, If I can get some time down the road, I'd like to implement some basic dom manipulation functions. Personally I see Lumen as the best means to do mobile app development in Arc (which is probably one of the best things that can happen for Arc IMHO). Arc on the server side, Lumen on the client side and a code base that's useable by both would be really nice.

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2 points by shawn 157 days ago | link

Correct! https://github.com/lumen-language is to lumen as to https://github.com/arclanguage is to arc.

ycombinator.lol is just because fixed-point combinators are funny:

  (define Y (λ(b)((λ(f)(b(λ(x)((f f) x))))
                  (λ(f)(b(λ(x)((f f) x)))))))
It's amusing that it's even possible, and it looks visually like what happens when you accidentally `cat` a binary file to your terminal.

EDIT: I typo'd the link; The magic trick is at https://news.ycombinator.com/item?id=17963471.

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2 points by akkartik 157 days ago | link

> https://github.com/lumen-language is to lumen as to https://github.com/arclanguage is to arc.

Touche :) It would be a little clearer if the contributors for the organization were public.

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2 points by shawn 157 days ago | link

Wanna see a magic trick? ...

Whoops, wrong link! It's at https://news.ycombinator.com/item?id=17963471.

It was delightful to discover how to pull that off. Hopefully it sounds as exciting as it felt.

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2 points by aw 160 days ago | link

The first question I'd ask is, what kind of language do you want to create?

That makes it a lot easier to answer a question like "Is X a good choice for Y?" It depends on Y! :-)

Then, along with asking here (which is fine), you might also want to ask the Racket folks. Go to https://racket-lang.org/ and scroll down to "Community". Then you can ask, "I'd like to create a language like Y, would Racket be a good choice? If so, how would I go about it?"

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