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What's wrong with Hindley-Milner?

• skybrian 5mo ago
  Leaving out types in public API's makes type errors hard to understand. Types should be declared in the API and bidirectional type inference used in the implementation. https://jimmyhmiller.com/easiest-way-to-build-type-checker https://jimmyhmiller.com/easiest-way-to-build-type-checker
  • josephg 5mo ago
    Eh. This causes some problems for rust. Right now you can have a function return impl Trait instead of a concrete type. Very handy - and essentially required by async functions. But the language also requires that types have names in lots of places. For example, you can't store an 'impl Trait' in a struct. You can't make a type alias of an impl Trait. And so on. As a result, async rust can only interact with a butchered subset of the language. (You can work around this with Box<dyn Future<...>> but performance suffers.) There's a proposal[1] to fix this. But the proposal has been under discussion for (checks watch) 7 years now. Until this lands, async remains a second class citizen in rust. This entire problem stems from rust's early decision to requiring concrete types at interface boundaries. https://github.com/rust-lang/rust/issues/63063 https://github.com/rust-lang/rust/issues/63063