Ah, I get it. I suppose typing is one of the big issues affecting speed. If the language standard insists on dynamic typing, there might be no way to get certain kinds of optimizations.
And yeah, call/cc is probably always going to be a bear. But man is it cool. :)
I suppose this goes against what a few of us (including me) were saying above -- that the language and the speed are really separate issues. Or maybe it's more coherent to say that language standards (as opposed to "languages" generally understood) can have a profound effect on speed. If they don't give implementors a lot of choice, they can box people into certain corners.
It's interesting that Scheme actually mandates optimization in at least one case (tail recursion). I don't know how many language standards make those kinds of demands, but I suspect there aren't many.
Tail recursion is interesting as it is not especially an optimization for speed but as a way to make programmers rely primarily on functional programming : if you don't have it, functional programming is rapidly a dead-end as you can make the stack explode really fast. As a bonus, it is faster :)
