This argument seems strange. When people complain that tests take a long time to perform, the argument usually falls back to "if your tests are useful, the time spent running them is well spent." Seems the same applies here. Scala takes a long time to compile if you lean heavily on the type system. This makes sense, since the type system can be seen as a type of test system.
So, if you are making useless types, the speed concern is likely best addressed by moving stuff out of the type system. If the extra time is preventing bugs, then few would argue it is wasted.
Typechecking shouldn't take much of the time. I'd wager (having never even looked at the Scala source code) that the time consuming part is compiling everything into JVM bytecode.
Since the type system in Scala is popularly touted as Turing complete, I think you are mistaken in this wager. I remember in one of the exercises for the course, I did something where compilation never terminated. Changed the type of a single function, and compilation took less than a second.
> Since the type system in Scala is popularly touted as Turing complete
So is GHC's. Turing-Completeness says nothing about speed, only about termination prediction. GHCi can type check most codebases in much less than a second. The puzzling thing about the apologism for Scala's slow speed is that some people seem to think that no FP language has ever had a fast compiler before...
Meh, the puzzling thing about many acolytes of anything in programming is the belief that all things have been solved. Usually best in what they care for most.
Clearly, since my point was easily shown as a non-sequitor, I'm not an expert. Following the folks involved with Scala, on the other hand, I don't have any reason to feel that they are the rank amateurs that they would have to be to be to produce such a slow compiler with no need.
My hunch, the support of nominative subtyping is the culprit. My backing for this? Pretty much nothing other than snippets of posts others have made.
So, if you are making useless types, the speed concern is likely best addressed by moving stuff out of the type system. If the extra time is preventing bugs, then few would argue it is wasted.
Or am I completely off in my view?