First. Thankyou for taking the time to respond to this. It is appreciated.

Aiui, if the leading candidates for a dispatch only use static nominal typing (specifying types like int, Int, Str, a class, role, etc. for their parameters) then resolution of which to finally pick is done at compile-time.

That implies that if I call a multi-sub defined to take (say) two Int vars; but I pass it integers embedded in ordinary scalars; then it will fail? What if the integers are being stored as strings in the PV of the scalar?

If Perl6 is to retain scalars; but people write their modules using Ints & Strs etc. for efficiency; then it either forces their users to also use Ints & Strs etc. or multi-subs will have to use runtime resolution.

Alternatively, I guess the programmers could add more multi-subs for each of the permutations of combinations of subscalar types and defined types; but that is a combinatorial nightmare.

Of course, this still leaves the gulf (an order of magnitude? two?) between the basic sub call performance of Rakudo and of perl.

Aiui there are tons of bog standard optimization techniques (speed and RAM usage) that still haven't yet been applied to Rakudo, NQP, and MoarVM. Aiui more of these optimizations are supposed to arrive this year but most will come in later years.

That's understandable, it took Java many years and iterations to sort out their performance problems; and they basically had to invent(*) (or at least, radically refine and generalise) JIT compilation to do it.

But my gut feel is that there are several Perl6 design elements Multi-subs, junctions, autothreading, to name but 3 -- that individually make writing an efficient runtime implementation exceedingly hard.

And writing a single VM to deal with all of those; plus the ability to introspect and reflect on everything including the kitchen sink; the neighbours dog; uncle Tom Cobbly an'all; makes for ... well, what we've seen till now.

I am aware smalltalk had a form of JIT before Java; and of course, LISP did it first; but Java refined it, generalised it, popularised it, and brought it to the main stream.