Julia is another contender. Julia code can be as performant as C++ code, but Julia code may be even more elegant than C++. Even without accounting for Julia's metaprogramming features, the compile-time expressiveness is top-notch.
It shares some of the same drawbacks as C++, though. The language is extremely powerful, so while it is easy to write performant code, it is also easy for non experts to write very suboptimal code.
> Number isn’t an interface—there are no operations common to all numbers.
When creating a new type, it should be more clear cut when is subtyping Number (or Real, etc.) valid. Should unitful quantities be numbers? Should intervals be numbers? Related: I think there are some attempts by Tim Holy and others to create/document "thick numbers".
Furthermore, I believe it might be good to align the Number type hierarchy with math/abstract algebra as much as possible without breaking backwards compatibility, which might making Number, or some subtypes of it, actual interfaces.
> Subtyping Number is a way to opt into numeric promotion and a few other useful generic behaviors. That’s it.
I don't think testing against every existing dependent would make sense currently. The issue is the lack of tooling for mechanically checking whether the dependent accesses implementation details of the dependency, in which case it would be valid for the dependency to break the dependent.
There are some proposals to forbid the registration of a package release which trespasses on the internals of another package, though.
I hope someone tackles the above sooner or later, but another issue is the approach of testing every known dependent package might be very costly, both in terms of compute and manual labor, the latter because someone would have to do the work of maintaining a blacklist for packages with flaky unit tests. The good news is that this work might considerably overlap with the already existing PkgEval infrastructure. We'll see.
What I wanted to say is that I'm skeptical regarding "interfaces", either as a language feature or as a package. Although TBH I have not yet given any specific "interfaces" design more than a cursory glance, so my position is not really justified.
> the culture of not prioritizing correctness in computation
On the contrary, it is my impression the experienced Julia programmers, including those involved in JuliaLang/julia, take correctness seriously. More so than in many other PL communities.
> there are people working on traits/interfaces - but these are still peripheral projects and not part of the core mission to my knowledge
What exactly do you mean by "traits" or "interfaces"? Why do you think these "traits" would help with the issues that bug you?
The Julia world is already quite careful with testing and CI. Apart from the usual unit testing, many packages do employ integration testing. The Julia project itself (compiler, etc) is tested against the package ecosystem quite often (regularly and for select pull requests).
Julia is not without warts, but this blog post is kinda rubbish. The post claims vague but scary "correctness issues", trying to support this with a collection of unrelated issue tickets from all across Julia and the Julia package ecosystem. Not all of which were even bugs in the first place, and many of which have long been resolved.
The fact that bugs happen in software should not surprise anyone. Even software of critical importance, such as GCC or LLVM, whose correctness is relied upon by the implementations of many programming languages (including C, C++ and Julia itself), are buggy.
Instead the post could have focused more on actual design issues, such as some of the Base interfaces being underspecified:
> the nature of many common implicit interfaces has not been made precise (for example, there is no agreement in the Julia community on what a number is)
The underspecified nature of Number (or Real, or IO) is an issue, albeit not related with the rest of the blog post. It does not excuse the scaremongering in the blog post, however.
It shares some of the same drawbacks as C++, though. The language is extremely powerful, so while it is easy to write performant code, it is also easy for non experts to write very suboptimal code.