continuation?

[Seong-Kook Shin]

Hi.

First of all, I have to say thank you very much those whom
have answered my trivial questions so far.

I cannot understand what the meaning of `continuation', and
how to do with `call-with-current-continuation'.

I've read several guile documents in addition to the book,
`The Scheme Programming Language -ANSI SCHEME-', but
I could understand neither.

Is there anyone can explain the basic idea of `continuation'
and can show some simple, brief and fullly explained example?
Or just let me know which document or book will be a good start.

In addition, the book says:

        call/cc must be passed a procedure P of one argument.
        call/cc obtains the current continuation add passes
        it to P.  The continuation itself is represented by a
        procedure K.  Each time K is applied to a value, it
        returns the value to the continuation of the call/cc
        application.

(1) What's the exact meaning of `application' in the above
   quotation?  I suppose that meaning might be the same which
   can be found in the Scheme grammer (also found in the book):

        <application> -> (<expression> <expression>*)

    Right?

(2) What's the exact meaning of *CURRENT* continuation?
   Does it mean the expression that will be evaluate next?
   For example:

        (call/cc
          (lambda (k)
            (* 5 (k 4))))
        =>4

    I think that the `current continuation' of above code
    is "(call/cc (lambda ...))" itself. Right?

(3) What's wrong in this code?

        (call/cc
          (lambda (k)
            (* 5 k)))
        => ABORT: (wrong-type-arg)

In the code of question 2, 3, "call/cc" is an abbreviation of
"call-with-current-continuation" as you expected.


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