>My understanding was that tail recursion ( or its optimized implementation ) >gives a (properly written) recursive program the efficiency of an >iterative program. Yes, because such implementations avoid "real" recursion, i.e. when they encounter tail recursive function calls they do not push some kind of return address on a stack. Of course, such an implementation of tail recursion is desirable, but it is iteration, in fact. I just wanted to point out that recursion generally is not a benefit at all. It is also no special sign of functional programming languages, you can do recursion in most imperative languages as well. The good thing about functional programming languages is merely the fact that symbols are evaluated regardless wether they're bound to data or to a function. This allows high level of data and functional abstraction without having to extend the core language. BTW, with trow and catch it should theoretically be possible to implement multitasking. Does anybody know how the "evaluation loop" at top level of REBOL works? (not that I want to implement multitasking, that's far beyond my capabilities, I'm just curious...) Greetings, Erich
