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by jbandela1 3796 days ago
The last statement was more in regards to the Blub definition implied by the article. Of course, people who are immersed in programming language theory are not Blub programmers - they are aware of what is possible, but are also aware of the inherent tradeoffs.

With regards to Rust, do you have any idea when more meta-programming features like variadics and non-type template parameters might be available in the language (are we looking at months, years, or decades)? Rust, has a lot of features that really interest me, but seeing the tuple serialization code brought back bad nightmares of simulating variadic templates using macros in C++ before I had a compiler that supported C++11 variadics. To me, at least personally, it felt like a step backward from C++14, and kind of curtailed my enthusiasm for doing a deep dive into the language. My test for the power of a language's type manipulation is how easy is it to write an implementation of apply(Function f, Tuple t) which will call f with the values of t. I would be most interested to see how Rust will implement this kind of metaprogramming.
2 comments
steveklabnik 3796 days ago
Yeah, I agree with my sibling comment above that Blub is kind of a weak concept for this reason.

It's hard to say because the work for those features hasn't even been started; the MIR refactoring is still underway. Once that's done, RFCs for this stuff will start to appear, and we'll have a better idea of overall schedule. I would say that the current schedule is "longer than months, shorter than a few years".

I myself _really_ want higher kinded types, but at the same time, I would rather wait and do it right than rush and regret thing slater. We have a solid language as it is; the need to get these more advanced features is not particularly urgent, in my opinion. I like to think on the long scale when it comes to the language: if it's going to be around 40 or 50 years, we're in year one. There's plenty of time.

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pcwalton 3796 days ago
> My test for the power of a language's type manipulation is how easy is it to write an implementation of apply(Function f, Tuple t) which will call f with the values of t. I would be most interested to see how Rust will implement this kind of metaprogramming.

That's kind of a weird litmus test of the power of the language's type manipulation: it only applies to languages where functions take multiple arguments, it's a pretty niche use case (since the workaround in Rust is straightforward), and there's nothing particularly sophisticated about variadic generics (what you need to solve the problem). I could equally say that my litmus test of a language's generics system is whether the compiler prevents errors during template expansion.

Anyway, to answer your question: that's really easy in Rust, as long as you're on nightly. The FnMut trait (and friends) allow you to call functions with tuples as arguments. https://doc.rust-lang.org/std/ops/trait.FnMut.html

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