scala/scala

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Ichoran

@Ichoran

Honestly I'm rather puzzled by why this is an interesting thing to do. Rust as a DSL hardly makes sense, since aside from its superior ability to infer types, and its lifetime/ownership system, its syntactic capabilities are basically a subset of Scala's.

Usually you want DSLs because they can express something that the original language can't easily express.

Klas Segeljakt

@segeljakt

the DSL is only meant to generate Rust code

Ichoran

@Ichoran

Ah, okay.

I am not sure why you would want to generate Rust code from a Scala DSL (as opposed to from a Rust DSL, for instance), but at least it sounds possible :)

Having a Rust backend to the Scala compiler would be interesting. Weird, but interesting.

Klas Segeljakt

@segeljakt

it will be for a stream processing engine, when it gets an incoming query it will generate Rust code for it and execute

Ichoran

@Ichoran

Okay, but why not write it all in Rust?

Klas Segeljakt

@segeljakt

Rust is not as good as Scala for meta-programming in I think

Ichoran

@Ichoran

Having to keep two nontrivial languages deeply in mind simultaneously to complete the project is not going to be easy.

Klas Segeljakt

@segeljakt

true

Ichoran

@Ichoran

I guess I'd agree with that. If all else was equal I'd use Scala.

Klas Segeljakt

@segeljakt

the code generator is a small part of the project

Ichoran

@Ichoran

Okay. Well, I guess if the project is already irrevocably committed to using both Scala and Rust, may as well charge ahead.

Klas Segeljakt

@segeljakt

the driver will be written in Scala and do most of the coordination, then the workers do the work in Rust

Ichoran

@Ichoran

Wouldn't be my first choice, but there are other choices that people make all the time that would be waaaaaay lower down on my list (like using Java to create and execute Java).

Klas Segeljakt

@segeljakt

lol

They put a JVM in the JVM?

Rob Norris

@tpolecat

Hm I think Scala is not very good for metaprogramming, depending on how you define it I guess.

The Scala macro system is a garbage fire.

I think it's pretty good for embedded DSLs though.

Seth Tisue

@SethTisue

What metaprogramming support exists in Rust?

Long Cao

@longcao

Rust has macros and derivation, not sure how that lines up with what's available in Scala https://doc.rust-lang.org/book/second-edition/appendix-04-macros.html

Gabriel Claramunt

@gclaramunt

give me a collapsing tower of interpreters :)

Klas Segeljakt

@segeljakt

Rust’s macros are not on the same level as Scala’s I think

the macros define meta-variables which can be substituted for token-trees

Separators, like (), {}, [] create token trees

Rob Norris

@tpolecat

@gclaramunt o/

Harrison Houghton

@hrhino

Sounds kinda like Dotty LMS, then?

Elikar Ibn Mtsouko

@mtsouko_twitter

What is a good rule of thumb to follow when creating a trait vs abstract class? It seems there is a good amount of overlap in functionality ...

Li Haoyi

@lihaoyi

Python’s metaprogramming is the best :D

it even has hygienic quasiquotes

i think ichoran was talking about runtime java source code generation and compilation

although i have put a jvm inside a jvm and it’s awesome(ly slow)

Li Haoyi

@lihaoyi

spark does runtime java source generation and it’s not bad; compiles fast enough, JITs down to fast assembly and is easier for most people to debug than malformed blobs of bytecode

Klas Segeljakt

@segeljakt

What does hygienic mean?

with quasiquotes :D

Li Haoyi

@lihaoyi

it means when you call a function foo in a quasiquote, the macro generated code calls the function foo that is lexically in scope where the quasiquote was defined, not whatever random foo may be in scope at the macro callsite

Gabriel Claramunt

@gclaramunt

@mtsouko_twitter since you can only mix one abstract class and many traits as you want, I try to use traits as much as I can... abstract classes is for when you really want OO and is a reasonable hierarchy

Justin du Coeur, AKA Mark Waks

@jducoeur

Yeah -- I tend to favor traits by default, unless I want constructor parameters or have some other reason to specifically want a class.

Fabio Labella

@SystemFw

abstract classes can have parameters, that's a big point (it will change though). They are also better for bincompat in 2.11, if you're writing a library

Rob Norris

@tpolecat

Once trait parameters exist get ready for "why do we even have classes?"

Elikar Ibn Mtsouko

@mtsouko_twitter

What were the design reasons behind not giving traits parameters in the first place?

Rob Norris

@tpolecat

Same reasoning as class/interface in Java I imagine.

nafg

@nafg

@klassegeljakt if the reason is JVM startup time, you may want to look into scala-native or Graal VM

Klas Segeljakt

@segeljakt

Ok I'll take a look

If you know any more libs please let me know 🙏

Rob Norris

@tpolecat

I guess I should own up to writing a cursed DSL. Take it as a warning https://github.com/tpolecat/basic-dsl

Miguel Pérez Pasalodos

@mpasa

That is just great :smile:

Hanns Holger Rutz

@Sciss

Is there a way to constrain a Double to "just smaller than 1.0" such that (aDouble * aPositiveInt).toInt < aPositiveInt is guaranteed to hold? I.e. I don't want to perform that check after each multiplication. Like I can empircally get a very long literal:

assert (0.999999999999999944488848768742172978818416595 < 1)

assert ((0.999999999999999944488848768742172978818416595 * Int.MaxValue).toInt < Int.MaxValue)

But I wasn't patient enough to keep looking for the digits (seems there are more)

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