Comment by cfallin | Hacker News Reader

Comment by cfallin | Hacker News Reader

Parent Full thread

Not at all -- there's a lot of commonality in the language designs.

Core language features: both have algebraic datatypes like ML ("case classes" in Scala, enums in Rust), and a 'match' statement that makes working with them easy. Both have pervasive destructuring that works with match arms, 'let' bindings, etc.

Data structures and mutation: both encourage a pragmatic version of immutability -- use values and provide functional interfaces primarily, but support mutation where needed. In Rust there are 'Cell' and 'RefCell' types, just like ML's cell-based interior mutability.

Library idioms: all three have the standard set of functional-style higher-order transformation functions ('map', 'filter', etc. -- Rust in particular has a very rich Iterator trait API), and it's idiomatic to use these.

FWIW, Rust's first/bootstrap compiler was written in OCaml and there's a lot of obvious influence.

I'm aware that Rust's bootstrap compiler was written in Ocaml. And yes, there are lots of ML inspirations in the language -- but not enough to make an ML language. Where are the module functors, for example? Many would consider that an essential element of an ML language, and it is a stretch to call a language an ML family member without them.

I don't want this to devolve into a No True Scotsman debate, I just feel that the parent post -- which decried a lack of similarity between Rust and Scala because they were both in the ML family -- was founded on a weak premise.

I think ML-family is fine. Scala is much closer to ML than what people sort into the Algol-family or C-family groups.

A module functor is nothing more than a higher order module...one that takes as a parameter some data structure that conforms to an interface (signature). Rust may not have constructs called module functors, but it definitely has constructs that are capably equivalent, as well as some that are even more powerful (a claim that applies to Scala as well)

For me, type inference, strong typing, and ADTs with pattern matching puts a language into the ML family quite easily.

All right, I concede.:) Thanks for sharing your views.

I mean, Haskell doesn't have module functors, and I'd certainly claim Haskell is in the ML family. If Haskell isn't, what would be?

Module functors were an SML feature - not really in the original 'ML' language. I would put Haskell in the ML family, and it doesn't have module functors. Rust has type inference, and a core type syntax and semantics that is heavily inspired by it.

Reply on news.ycombinator.com