Hacker News Reader

Comment by svieira | Hacker News Reader

There are several languages that are working on solving the composable effects problem that I am aware of:

* Pony - capabilities based language inspired by `E`. Effects are like Rust's (provided by the language, not extensible by end users): https://www.ponylang.io/

* Koka - effects are first class and higher order. `filter` is a higher order function that is "effectfully parameterized" as well as "parameterized over its types". Effects can be discharged at any level of the program and the effects "stack" is manipulable (in what appears to be a principled way) https://koka-lang.github.io/koka/doc/index.html

* Multi-core OCaml is also building parallelism on a version of effects that looks quite a lot like Koka (though I'm not familiar enough with it to say how close they are in practice).

What other ones am I missing?

View on HN

Flix: https://flix.dev/

(edit) c'n'p from their site:

Why Flix?

Flix aims to offer a unique combination of features that no other programming language offers, including: algebraic data types and pattern matching (like Haskell, OCaml), extensible records (like Elm), type classes (like Haskell, Rust), higher-kinded types (like Haskell), local type inference (like Haskell, OCaml), channel and process-based concurrency (like Go), a polymorphic effect system (unique feature), first-class Datalog constraints (unique feature), and compilation to JVM bytecode (like Scala).

Honestly, I find the announcements of 99% of new languages here at hackernews pretty boring, because they all feel like they didn't learn anything from the last 20 years or so.

But this list actually makes me excited!

Yeah, me too. They published quite a lot of papers using it [0]. The datalog integration is pretty nice too, haven't gotten to learning Prolog yet, but seeing how concise a sudoku solver can be implemented in it was an experience.

(edit) you can import Java, Kotlin and Scala in it too, those are automatically Impure. Would enable purely functional architecture [1] and falling into the "Pit of success" [2].

[0] https://flix.dev/research/ [1] https://blog.ploeh.dk/2016/03/18/functional-architecture-is-... [2] https://www.youtube.com/watch?v=US8QG9I1XW0

Thanks for the link. Indeed a nice programming language proposal. I love the opinionated set of design principles https://flix.dev/principles/.

There is also a former thread on HN: https://news.ycombinator.com/item?id=25513397

Very nice, good catch. It has UFCS [0] like D!

[0] https://en.wikipedia.org/wiki/Uniform_Function_Call_Syntax

Let me tell you what I'm worried about with effects systems: One of the smartest people I know of has a library called Eff https://github.com/hasura/eff that efficiently implements effects through some modifications to GHC. The thing is, she's pretty much stopped working on because she found some really nasty semantic edge-cases that she couldn't resolve to her satisfaction. (I don't understand the problems well enough to describe them, and I think they're specific to lazy languages, but it has left me cautious about the effect model in general.)

Does she have any writings online that describe those nasty semantic edge-cases?

Unfortunately, mostly Twitter, and that’s profoundly unsearchable. Here’s the original announcement before it ran aground: https://mobile.twitter.com/lexi_lambda/status/12262098236640...

What makes you say it ran aground? I thought it was just waiting for [0].

[0]: https://github.com/nicuveo/ghc-proposals/blob/master/proposa...

Freer Monads, More Extensible Effects

http://okmij.org/ftp/Haskell/extensible/more.pdf

Frank: https://github.com/frank-lang/frank

Seams stale. The paper is a joy to read though...

"Do, be, do, be, do" (those who read it will understand)

This paper really opened my eyes for what's possible.

Frank does it right, yes.

They use "abilities" as a dual to effects. That's imho the crucial part. Most of the other effect systems only implement half the thing.

But I would change two parts: First of all the co-effects should be proper "capabilities" in the sense of "capability security". The other thing would be modelling the co-effects as co-data. They already use some (ad hoc?) notion of "Interfaces". Those look like co-data definitions (resembling OOP Interfaces). I also thing co-data with co-pattern matching could solve some of the problems mentioned at the end of the paper. Inspiration could be taken form: https://www.cs.uoregon.edu/Reports/DRP-201905-Sullivan.pdf

Unison has an algebraic effect system, under the name "abilities"

https://www.unisonweb.org/docs/abilities/

How about the languages that have already "solved" the problem (in terms of ergonomically usage), such as Haskell, Purescript, Scala and a lot of other niche languages?

That being said, Rust has a bit of a harder time due to the focus on performance and optimally zero-cost abstraction, whereas other languages are more lenient and focus rather on expressiveness and composability / code reuse.

Well, more attempts at this problem come along pretty often (speaking for Haskell at least, and I expect those attempts to be more mature than the other languages you mentioned), so I don't think you can say those languages have solved it. Like the other comment mentioned, it's an active area of research, and some of the research happens in languages designed to solve that problem, and some happens in languages that support solutions to the problem.

(Just to add- there's a really wide range of ergonomics that you can support and it's hard to get everything right. And performance is super tricky!)

I mean, monads famously don't compose - you have to write a bunch of monad transformers.

True, but not a huge real world issue in nearly all the relevant cases.

I can very easily have a fallible, asynchronous, multi-value, stateful, database connected computation that returns a Bool and use it in let’s say ‘filterM’.

Most transformers are already written for me.

Edit: switching between no effect and some effect is the tricky part though.

I find in practice that even though I don't have to write the transformers myself, `lift`ing and `unlift`ing things is a pain in the ass. Once you try a proper algebraic effect system, it's hard to feel like transformers are an adequate solution.

Most of the relevant plumbing is generic though. Check out ZIO or cats-effect in Scala which I think both provide highly composable effect systems.

Does Idris qualify?

https://www.idris-lang.org/

Idris is great.

https://nim-lang.org/docs/manual.html#effect-system

F* (f star) too! https://www.fstar-lang.org/

Maybe also ATS, but I'm unsure if it qualifies

Last I looked, Ocaml's upcoming effect system is untyped, so doesn't really belong in the discussion.

Upcoming OCaml multicore won't expose effects at all. I believe the intention is to finish work on typed effects[1] and only then add it to the language.

[1]: https://www.janestreet.com/tech-talks/effective-programming/

They have an effects branch but admitted it won't be ready in time for OCaml 5.0 (supposedly arriving around end of 2021 / early 2022) so they have a separate compiler variant with it where the progress can be tracked.

Last I read, they really want to nail down the entire multi-threaded environment to the last detail first (which mostly means make sure no parallel bugs are introduced + single-threaded code won't become slower; both pretty huge goals).

It's not quite built into the language but Scala has a really well-developed ecosystem of effect libraries (ZIO, Monix, cats-effect) that solve this problem really nicely.

There's also the Eff programming language: https://www.eff-lang.org/

Koka looks very promising to me. I wonder why it’s not getting more attention. Probably because of being research at this point.

Did not MSFT pull funding?

Oh didn’t know that. Sad to hear that :(

Reply on news.ycombinator.com