Is it possible to use continuations to make foldRight tail recursive?

Question

The following blog article shows how in F# foldBack can be made tail recursive using continuation passing style.

In Scala this would mean that:

Answer 1

Why is this not a problem with F#?

F# has all tail calls optimized.

And is there any way to work around this with Scala?

You can do TCO using other techniques like trampolines but you lose interop because it changes the calling convention and it is ~10× slower. This is one of the three reasons I don't use Scala.

EDIT

Your benchmark results indicate that Scala's trampolines are a lot faster than they were the last time I tested them. Also, it is interesting to add equivalent benchmarks using F# and for larger lists (because there's no point in doing CPS on small lists!).

For 1,000x on a 1,000-element list on my netbook with a 1.67GHz N570 Intel Atom, I get:

List.fold     0.022s
List.rev+fold 0.116s
List.foldBack 0.047s
foldContTC    0.334s

For 1x 1,000,000-element list, I get:

List.fold     0.024s
List.rev+fold 0.188s
List.foldBack 0.054s
foldContTC    0.570s

You may also be interested in the old discussions about this on the caml-list in the context of replacing OCaml's non-tail-recursive list functions with optimized tail recursive ones.