> (6) any good readable references that explain it lucidly ? This was something that has been very interesting to me for a while now, and I'm actually still having a difficult time wrapping my head around it completely.
The best written explanation that I've come across was in "The Scheme Programming Language" (http://mitpress.mit.edu/catalog/item/ default.asp?ttype=2&tid=9946). But perhaps others have better references. I'll attempt my own little explanation of call/cc. I'll butcher some of it, I'm sure, but hopefully those more knowledgeable will politely correct me. I will start with a loose analogy and point out a couple examples I came across that did make a lot of sense. First, the bad analogy I have (if you are coming from C programming like me) is setjmp and longjmp. This is a bad analogy in that you're talking about hardware and stack states as opposed to functions, but a good analogy in that it saves the current state of execution, and returns to that same state at a later time with a piece of data attached to it. My first example of using this would be to create a return function in Scheme. I hope I don't get this wrong, but the example would be something like this: (define (my-test x) (call/cc (lambda (return) (return x)))) Now, here's my understanding of what is happening under-the-hood: 1. call/cc stores the current execution state and creates a function to restore to that state. 2. call/cc then calls its own argument with the function it created. The key here is that "return" is a function (created by call/cc) taking 1 argument, and it restores execution at the same state it was when the call/cc began (or immediately after it?). This line: (return x) is really just calling the function created by call/cc, which will restore the execution state to what it was just prior to the call/cc, along with a parameter (in this case, the value of x). My next example I don't follow 100%, and I won't attempt to reproduce it here, but it generates a continuation that modifies itself (bad?) to define a list iterator. http://blog.plt-scheme.org/2007/07/callcc-and-self-modifying-code.html I recommend putting that code into a Scheme interpreter and running it. You'll get it. Hope this helps, and I look forward to better explanations than mine that will help me along as well. :) Jeff M. -- http://mail.python.org/mailman/listinfo/python-list
