Re: The fundamental concept of continuations

[Bakul Shah <usenet@bitblocks.com>]

gnuist006@gmail.com wrote:
 > Again I am depressed to encounter a fundamentally new concept that I
 > was all along unheard of.

The concept is 37 years old.  Wadsworth in his "Continuation
Revisited" paper says he & Strachey were struggling with
extending the technique of denotational semantics to describe
jumps and not finding a satisfactory answer.  Then, in his
words:

   in October 1970 Strachey showed me a paper "Proving
   algorithms by tail functions" by Mazurkiewicz [2] which he
   had obtained from an IFIP WG2.2 meeting. Just the phrase
   "tail functions" in the title was enough -- given the
   experience of our earlier struggles -- for the ideas to
   click into place! The (meaning of the) "rest of the program"
   was needed as an argument to the semantic functions -- just
   so those constructs that did not use it, like jumps, could
   throw it anyway. The term "continuation" was coined as
   capturing the essence of this extra argument (though I
   often wished to have a shorter word!) and the rest, as they
   say, is history.

 > Its not even in paul graham's book where i
 > learnt part of Lisp. Its in Marc Feeley's video.
 >
 > Can anyone explain:
 >
 > (1) its origin
 > (2) its syntax and semantics in emacs lisp, common lisp, scheme
 > (3) Is it present in python and java ?
 > (4) Its implementation in assembly. for example in the manner that
 > pointer fundamentally arises from indirect addressing and nothing new.
 > So how do you juggle PC to do it.
 > (5) how does it compare to and superior to a function or subroutine
 > call. how does it differ.
 >
 > Thanks a lot.
 >
 > (6) any good readable references that explain it lucidly ?

You might like this one:

http://www.intertwingly.net/blog/2005/04/13/Continuations-for-Curmudgeons