callcc

The Wikipedia article on Continuation says: "In any language which supports closures , it is possible to write programs in continuation passing style and manually implement call/cc ." Either that is true and I need to know how to do it or it is not true and that statement needs to be corrected. If this is true, please show me how to implement call/cc in Lua because I can't see how. I think I'd be able to implement call/cc manually if Lua had the coroutine.clone function as explained here . If closures are not enough to implement call/cc then what else is needed? The text below is optional

I've tried several times to grasp the concept of continuations and call/cc . Every single attempt was a failure. Can somebody please explain me these concepts, ideally with more realistic examples than these on Wikipedia or in other SO posts. I have background in web programming and OOP. I also understand 6502 assembly and had a minor randez-vous with Erlang. However still, I can't wrap my head around call/cc. temoto Look, i've found this Continuation Passing Style best description on this topic. Here's stripped of details copy of that article: Author: Marijn Haverbeke Date: July 24th 2007

After reading The Seasoned Schemer I felt I understood call/cc properly. But, after seeing some WOW tricks with call/cc I found I was wrong. (define cc 0) (define (f) (call/cc (lambda (k) (set! cc k) 3))) (+ 1 2 4 (f)) ; eval's to 10 (cc 13) ; eval's to 20 That perfectly match my understanding. I think when I reach a call/cc call I am just saving the program state. and calling the function next to it with a function. If that function ( k ) is called from somewhere than I just replacing the entire (call/cc ...) stuff with the parameter given to it. The above program seems to worked that way too

I've been following the new announcement regarding the new async feature that will be in c# 5.0. I have a basic understanding of continuation passing style and of the transformation the new c# compiler makes to code like this snippet from Eric Lippert's post : async void ArchiveDocuments(List<Url> urls) { Task archive = null; for(int i = 0; i < urls.Count; ++i) { var document = await FetchAsync(urls[i]); if (archive != null) await archive; archive = ArchiveAsync(document); } } I know that some languages implement continuations natively, via call-with-current-continuation ( callcc ), but I don