Towards Scala 3 • Hacker News Board

Re: Towards Scala 3

#381

Post by YorkshireSeason » Thu, Apr 26, 2018, 10:49 AM UTC

lptk wrote: post #358

YorkshireSeason wrote: post #153

Earlier quoted context omitted.

From an abstract PL theory POV, Haskell's key innovation over ML was HKTs. It was an experiment at the time, but one that was successful beyond all expectation: I cannot imagine designing a new PL without HKTs. (Note that Rust is also trying to add HKTs, but has been running into difficulties with type-based lifetime tracking IIRC.) Implicits are a generalisation of default arguments (I don't know where they were pio…

> Haskell's key innovation over ML was HKTs In fact, ML modules have had higher-kinded types [1] since before Haskell even existed. I guess Haskell's main innovation in this domain is really its very convenient higher-kinded parametric polymorphism with type classes. [1] MacQueen, D B (1984). Modules for Standard ML. Conference Record of the 1984 ACM Symposium on LISP and Functional Programming Languages. 198-207.

Thanks. That's really interesting. I need to read MacQueen's paper. Is this full HKT, in the sense that all constructions wiht HKTs can be encoded in MacQueen's system?

Re: Towards Scala 3

#382

Post by lptk » Mon, Apr 30, 2018, 10:09 AM UTC

YorkshireSeason wrote: post #381

lptk wrote: post #358

Earlier quoted context omitted.

> Haskell's key innovation over ML was HKTs In fact, ML modules have had higher-kinded types [1] since before Haskell even existed. I guess Haskell's main innovation in this domain is really its very convenient higher-kinded parametric polymorphism with type classes. [1] MacQueen, D B (1984). Modules for Standard ML. Conference Record of the 1984 ACM Symposium on LISP and Functional Programming Languages. 198-207.

Thanks. That's really interesting. I need to read MacQueen's paper. Is this full HKT, in the sense that all constructions wiht HKTs can be encoded in MacQueen's system?

If by "all constructions wiht HKTs", you mean what can be done with HKTs in Haskell, then I'd say yes. It is well-known that ML modules provide a very advanced level of expressiveness, especially since OCaml's introduction of first-class modules. Also, Scala took this idea further and provides principled recursive first-class modules (which Scala calls dependent object types).

The problem is that modules in ML have a verbose syntax and are clunky to use compared to type classes. OCaml's modular implicits aim to make this better (see https://arxiv.org/abs/1512.01895), taking inspiration from Sala's implicits.

Re: Towards Scala 3

#383

Post by YorkshireSeason » Thu, May 03, 2018, 5:47 PM UTC

lptk wrote: post #382

YorkshireSeason wrote: post #381

Earlier quoted context omitted.

Thanks. That's really interesting. I need to read MacQueen's paper. Is this full HKT, in the sense that all constructions wiht HKTs can be encoded in MacQueen's system?

If by "all constructions wiht HKTs", you mean what can be done with HKTs in Haskell, then I'd say yes. It is well-known that ML modules provide a very advanced level of expressiveness, especially since OCaml's introduction of first-class modules. Also, Scala took this idea further and provides principled recursive first-class modules (which Scala calls dependent object types). The problem is that modules in ML have a…

I understand that making modules first-class gives them a lot of expressivity. But they are a fairly recent development" at least in OCaml the come much after Haskell. But are modules in MacQueen's sense first-class?