Yukihiro Matsumoto writes:
 > |2)the Kernel method  callcc.
 > 
 > It's a continuation.  If you know scheme's call/cc, that's it.  If you
 > don't know... hmm.. Could somebody explain it please?  Shugo?
 > 
Scheme's call-with-current-continuation lets interrupt a computation
at a certain point and makes it possible to reassume it at a later point.
It is usually implemented with setjmp() and longjmp(), wasting often
a lot of memory, just like making a fork() on the Unix system level
and switching between processes. It can be used to simulate parallel
processes at high cost (complete stack backup). It may also be used for 
purposes like jump instructions and exceptions, such as C's goto, return,
break, continue. Some scheme implementation nowadays provide lightweight
substitutes of several classical c/cc tasks. Another application is
backtracking, used for debugging purposes.

Klaus Schilling