Rust for Clojurists

https://gist.github.com/oakes/4af1023b6c5162c6f8f0

by jarcane • 11 years ago

84 33 11 years ago

gist.github.com

scribu• 11 years ago

Previously: https://news.ycombinator.com/item?id=9250020

I thought it wasn't possible to submit the exact same URL twice.

dagw• 11 years ago

There's a timeout of after which point you can submit a URL again.

edem• 11 years ago

They call themselves "clojurians" if I recall it right.

kul_• 11 years ago

clojurelings

jarcane• 11 years ago

Oakes literally wrote the Clojure IDE I use when I'm not on Emacs, so I figure he earned the right to call himself whatever he likes. ;)

pygy_• 11 years ago

This is a good introduction to Rust, regardless of your Clojure background (I read a few articles about it when it was trending on HN, but never wrote a line of Clojure).

JBiserkov• 11 years ago

Rust is statically typed. The upside is, you will curse it at compile-time instead of at runtime. The downside is, "exploratory programming" means exploring how to convince the compiler to let you try an idea.

alfiedotwtf• 11 years ago

For me, yes you will curse a lot at compile time. But the upside is that stupid, preventable programming errors (which are responsible for a majority of security vulnerabilites) are stopped at compile time, not at segfault time.

steveklabnik• 11 years ago

We've also found that people generally struggle at first, but at some point, you internalize the rules, and then they click, and you don't fight all that much anymore.

lambdaelite3• 11 years ago

Rust’s strengths are Clojure’s weaknesses, and vice-versa. Rust isn’t as expressive or interoperable, and its concurrency story isn’t as complete. That said, it’s much better for performance or safety critical needs, and it can be embedded inside other programs or on very limited hardware.

I find this hard to believe. Is anyone actually using Rust for a safety-critical application?

jamwt2• 11 years ago

Depends on what you mean by safety. "People may die" safety, no; but "data may be lost, existential risk to business" safety, yes. Dropbox is writing a block storage engine in it.

lambdaelite3• 11 years ago

I go by what I thought was the accepted definition, which is a failure or error presenting a risk for temporary or permanent harm to people. Financial risk like data loss would fall under mission critical.

discreteevent• 11 years ago

A lot of certified safe systems are written in C++. I mean the ones that control the machine that could kill you. Response time is often a critical factor in safe systems. Also languages aren't as important as we would like then to be. Proof isn't used much for example because proofs are too difficult to review. Other techniques are more important like review, redundancy and testing. Safe systems tend to be more about boring old software engineering than computer science.

lambdaelite3• 11 years ago

I agree, the choice of programming language is one of the less important parts of the SDLC. In the case of Rust for SC work, as the linked article alludes to, what doesn't make sense to me is that there is no industrial-grade tooling or support software. It seems like an ill-informed statement.

As to proofs, I thought some level of formal proof was required at SIL4?

mej10• 11 years ago

I write Clojure every day and love it. I'm interested in learning Rust, but I'd like to learn it via a project that I couldn't do effectively in Clojure. Any ideas?

grayrest2• 11 years ago

There aren't that many things you can't do in Clojure, the main place Rust has an edge is in efficiency. I plan on doing an Avro implementation but other projects (mostly work-related) have a higher priority.

In terms of larger projects, the Servo guys always seem to encourage people learning Rust to get involved. One of the projects I'm most interested in is Frank McSherry's timely/differental dataflow repos. I wanted a Rust implementation of Naiad when I first read the paper so I was quite pleased to see one of the authors do an implementation, even if it doesn't seem to be a full time pursuit.

[1] https://github.com/frankmcsherry/timely-dataflow/

Most first-rust-projects that are announced on reddit/discourse seem to be games (Piston), simple web apps, raytracers, or datastructures.

nickbauman3• 11 years ago

I love Clojure but it's unsuitable for realtime problems because of GC. For example, a programmable audio synthesizer. Audio signal processing has to be realtime or else it can't sync with the music playing. Rust may not be suitable for that either, but it seems like it's much closer to being able to do that than Clojure will be anytime soon.

bkeroack• 11 years ago

"You're in an industry reaping disproportionate benefit from loose money policies, leading to a trend-chasing culture of overpaid nerds making web apps."

This is how software engineers undervalue themselves and damage their own profession. You will never see doctors or lawyers write a statement like that about themselves.

The line about "loose money" is laughable to anyone who's ever actually tried to raise funding.

nickbauman3• 11 years ago

Agree. But there is an element of truth to it. And that same element can be applied to doctors and lawyers. Probably especially lawyers. Doctors and lawyers don't fundraise for themselves, either. They don't need to.

stcredzero2• 11 years ago

You will never see doctors or lawyers write a statement like that about themselves.

Really? I've often heard doctors and lawyers engage in a little self-aware self parody.

reitzensteinm• 11 years ago

Just because you found it hard doesn't disprove the statement. It could be harder still without said loose money.

kyllo2• 11 years ago

It's a joke ok? And have you never heard a lawyer joke before? A lot of lawyers laugh at them too.

This part was funnier though: Many people try to compare Rust to Go, but this is flawed. Go is an ancient board game that emphasizes strategy. Rust is more appropriately compared to Chess, a board game focused on low-level tactics.

moonchrome2• 11 years ago

I have this crazy idea that you could build Clojure on Rust the same way Clojure sits on top of JVM right now and it could provide you with some interesting benefits.

First of all Rust doesn't implement a GC but it has very precise memory management semantics which means integrating in to a GC should be possible and safe.

I believe Clojure immutable data structures would allow you to (theoretically) build a fast/simplified GC because immutable data has some very nice properties :

* no cycles except trough reference types which are explicitly marked - this means you never need to scan old generation to collect the new generation

* data is immutable which means copying can be done in parallel

* mutable references are explicitly marked and isolated which means you could have a very minimal pause to update references

And Rust could safely encode all those requirements in it's type system to make the interop safe. No need to sprinkle write barriers all over the place, localized and isolated mutable references (you can modify the update semantics and track them easily), minimal pause times, parallel collection, etc.

I think there are other interesting things you could do, for example Clojure is pretty static for a dynamically typed language and protocols map nicely to traits I wonder if you could somehow remove the dynamic typing and just have compile time type inference figure out the types (requiring explicit types when the system can't infer the types) - this would allow you to send Clojure down to LLVM along with Rust. Or maybe you could have an interpreter for the truly dynamic stuff - but then you'd need to figure out how to export metadata.

Also I'm sure that the only sane/safe way to do it would be to restrict the kinds of objects and that would require serious thinking too.

stcredzero2• 11 years ago

I have this crazy idea that you could build Clojure on Rust the same way Clojure sits on top of JVM right now and it could provide you with some interesting benefits.

If you read some of the design docs and articles, you'll find that Clojure is designed to be a "hosted" language from the ground up. It would be a challenge to implement some of Clojure's dynamic features. You could very well do a Clojure-like language which has a different approach to being functional. Clojure is very Lisp-y in that it's actually a dynamic runtime fronted by a language that makes it look functional.

tsmarsh• 11 years ago

I had similar thoughts but wanted to take it a step further and just have a GC less Clojure built on Rust. You would have to do things like nest functions inside of (ns), you couldn't have (def) but this is all before I've spent any real hammock time on it. If you get started it would be fun to follow / contribute to.

pron2• 11 years ago

this means you never need to scan old generation to collect the new generation

Even in HotSpot you don't need to scan the old generation if references in it don't change. You only scan (roughly) those old objects who hold references that have been mutated since the last collection.

data is immutable which means copying can be done in parallel

This is also possible when mutation is allowed (see Red Hat's Shenandoah[1][2], A new GC for HotSpot), and immutability doesn't make the challenge significantly easier (there is added overhead for mutation only).

mutable references are explicitly marked and isolated which means you could have a very minimal pause to update references... No need to sprinkle write barriers all over the place

Again, mutating reference fields has a special barrier in HotSpot's GCs, but they're not "sprinkled all over the place" -- they're as good as being specially marked.

To summarize, current (and future) HotSpot GCs punish you for mutation, but not for the possibility of mutation; you get all the benefits of immutability automatically when you simply don't mutate references. Immutability -- as you note -- might indeed simplify the GC (though not in the case of Clojure, which does allow quite a lot of mutability -- not everywhere, but enough that you have to account for it not as an outlier), but it doesn't make it faster.

----

for example Clojure is pretty static for a dynamically typed language and protocols map nicely to traits I wonder if you could somehow remove the dynamic typing and just have compile time type inference figure out the types (requiring explicit types when the system can't infer the types) - this would allow you to send Clojure down to LLVM along with Rust.

A good JIT (like HotSpot) does this a lot better. It is true that Clojure is nowhere near as crazily-dispatched as, say Ruby, but it does rely a lot on Java-like interface-based dynamic dispatch. If your type inference is really, really good, you might be able to identify a great deal of the monomorphic call-sites, but a good JIT finds all of them and makes those calls virtually free, something an AOT compiler can never hope to achieve. Besides, HotSpot's optimizing JIT is a state-of-the-art compiler. You won't do any better with LLVM.

There are approaches that are good for some languages, and others that are good for others. Language's that rely on dynamic dispatch are better off using a JIT than an AOT compiler (actually, pretty much every language would get better code generation with a JIT -- except C which hardly does any dynamic dispatch -- but a JIT has some runtime overheads in warmup, RAM and energy, and languages that don't do too much dynamic dispatch can get excellent machine code generated by an AOT compiler, so that a JIT isn't worth it).

----

In short, while you could (maybe) compile Clojure down to Rust, you'll see no benefit, and probably quite a few disadvantages to that approach. If you want Clojure-Rust interoperability, you can get it today with RustJNI[3].

[1] http://openjdk.java.net/jeps/189

[2] http://www.jclarity.com/2014/02/19/shenandoah-a-new-low-paus...

[3] https://github.com/Monnoroch/RustJni

moonchrome2• 11 years ago

Even in HotSpot you don't need to scan the old generation if references in it don't change. You only scan (roughly) those old objects who hold references that have been mutated since the last collection.
This is also possible when mutation is allowed (see Red Hat's Shenandoah[1][2], A new GC for HotSpot), and immutability doesn't make the challenge significantly easier (there is added overhead for mutation only).

You pay for this with barriers and implementation complexity.

To summarize, current (and future) HotSpot GCs punish you for mutation, but not for the possibility of mutation; you get all the benefits of immutability automatically when you simply don't mutate references. Immutability -- as you note -- might indeed simplify the GC (though not in the case of Clojure, which does allow quite a lot of mutability -- not everywhere, but enough that you have to account for it not as an outlier), but it doesn't make it faster.
A good JIT (like HotSpot) does this a lot better. It is true that Clojure is nowhere near as crazily-dispatched as, say Ruby, but it does rely a lot on Java-like interface-based dynamic dispatch. If your type inference is really, really good, you might be able to identify a great deal of the monomorphic call-sites, but a good JIT finds all of them and makes those calls virtually free, something an AOT compiler can never hope to achieve. Besides, HotSpot's optimizing JIT is a state-of-the-art compiler. You won't do any better with LLVM.

Rust code doesn't pay for write barriers at all - my point isn't that Clojure on Rust would be faster than Clojure on JVM, it's that Rust code allows much more deterministic performance, better tools for manual optimizations and native interop than JVM and you'd write the performance sensitive code in Rust. Clojure is then a high level tool to consume Rust code.

I think you're looking at this the wrong way and missing the obvious benefits - you would get a simple almost pauseless parallel GC and a high level language with trivial native/safe rust interop (which JNI isn't).

Because of Rust type system you could even isolate threads that have no access to the shared heap and not collect/pause on those - so no chance at pauses at all. And AoT compilation also gives you deterministic performance.

Anyway it would be a lot of work for sure, I doubt it would be a straight port of clojure (would need to make it more static to fit to AOT nicely) and you would have to modify Rust to generate metadata so that the dynamics parts could run (or just ditch the dynamic part completely and force everything to be resolved at compile time with a simplified/constrained type system that would be simpler to infer without explicit typing).

kyllo2• 11 years ago

It's an interesting idea, but the fact that the Rust compiler is an AOT compiler with an extremely minimal runtime makes it seem like a poor fit for Clojure which is very much an interpreter/REPL-driven language.

Rust for Clojurists

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