[art-w]

I agree that some language features have a binary nature, like static/overridable or lazy/strict, but maybe we shouldn't classify all of them like that?

The "new" keyword in Java is very much like the proposed "return from": if you know that something is an object, and that object allocation is always done on the heap, then Foo() is as clear as new Foo(). The "new" keyword is a residual from C++, where you actually had a choice. Is it possible that people don't dismiss Python for Java because of the lack of "new", but because its GC isn't as good?

If we had an hypothetical IDE that used colors to transmit static analysis to the user, then we could categorise the keywords between "this is something the IDE can infer" and "this is something the user should specify". Object allocation falls into the inferable (so rather than writing "new", the IDE would highlight the expression in red); virtual is not inferable; delay is not inferable; tail calls are inferable, and can be shown in pink or whatever.

Anyway, TCE is an optimization: we can run more programs faster when we have it. When we don't use tailrec, we still benefit from it as our program consumes less memory overall. The cost of tailcall elimination is purely cognitive, for people who learned the old C-like stack behaviour (but even C compilers handle TCE now.) If TCE/no-TCE matched the static/virtual and lazy/strict binary choice, then there would be situations were TCE has a negative impact on the code runtime.