Summary by Dan Luu on the question about whether for statically typed languages, objective advantages (like having measurably fewer bugs, or solving problems in measurably less time) can be shown.
If I think about this, authors of statically typed languages in general at their beginning might not even have claimed that they have such advantages. Originally, the objective advantage was that for computers like a PDP11 - which had initially only 4 K of memory and a 16-bit adress space - was that something like C or Pascal compilers could run on them at all, and even later C programs were much faster than Lisp programs of that time. At that time, it was also considered an attribute of the programming language whether code was compiled to machine instructions or interpreted.
Todays, with JIT compilation like in Java and the best implementation of Common Lisp like SBCL being at a stone’s throw of the performance of Java programs, this distinction is not so much relevant any more.
Further, opinions might have been biased by comparing C to memory-safe languages, in other words, when there were perceived actual productivity gains, the causes might have been confused.
The thing which seems more or less firm ground is that the less lines of code you need to write to cover a requirement, the fewer bugs it will have. So more concise/expressive languages do have an advantage.
There are people which have looked at all the program samples in the above linked benchmark game and have compared run-time performamce and size of the source code. This leads to interesting and sometimes really unintuitive insights - there are in fact large differences between code sizes for the same task between programming languages, and a couple of different languages like Scala, JavaScript, Racket(PLT Scheme) and Lua come out quite well for the ratio of size and performance.
But given all this, how can one assess productivity, or the time to get from definition of a task to a working program, at all?
And the same kind of questions arise for testing. Most people would agree nowadays that automated tests are worth their effort, that they improve quality / shorten the time to get something working / lead to fewer bugs. (A modern version of the Joel Test might have automated testing included, but, spoiler: >!Joel’s list does not contain it.!<)
Testing in small units also interacts positively with a “pure”, side-effect-free, or ‘functional’ programming style… with the caveat perhaps that this style might push complex I/O functions of a program to its periphery.
It feels more solid to have a complex program covered by tests, yes, but how can this be confirmed in an objective way? And if it can, for which kind of software is this valid? Are the same methodologies adequate for web programming as for industrial embedded devices or a text editor?
Because that’s very far from the only difference between Haskell and Rust. It’s other things that make Haskell a worse choice than Rust most of the time.
You are right in that it’s a spectrum from dynamically typed to simple static types (something like Java) to fancy static types (Haskell) then dependent types (Idris) and finally full on formal verification (Lean). And I agree that at some point it can become not worth the effort. But that point is pretty clearly after and mainstream statically typed language (Rust, Go, Typescript, Dart, Swift, Python, etc).
In those languages and time you spend adding static types is easily paid back in not writing tests, debugging, writing docs, searching code, screwing up refactoring. Static types in these languages are a time saver overall.
I really would like to believe that. And, as I said, I use Rust for larger, more complex programs with high requirements to performance.
But again, the statement in the second cited sentence - what proof does exist that this is true? I get that you can spend time and effort and get better correctness. I also get that better ergononics - like the far better error messages which the Rust compiler has compared to a C++ compiler - can possibly offset or perhaps even outweight the extra effort. And I think this probably increases with a programs size, complexity, and life time.
But to say it is always less effort if you use Rust or Idris, for any kind of program - I think that, even when subtracting the amount of becoming familiar with it, well this is a strong statement, and I’d like to see some evidence for it.
The evidence is that I have tried writing Python/JavaScript with/without type hints and the difference was so stark that there’s really no doubt in my mind.
You can say “well I don’t believe you”… in which case I’d encourage you to try it yourself (using a proper IDE and use Pyright; not Mypy)… But you can equally say “well I don’t believe you” to scientific studies so it’s not fundamentally different. There are plenty of scientific studies I don’t believe and didn’t believe (e.g. power poses).