Type of a continuation in Racket and determining current continuation

Question

What is the type of a continuation in Racket? And how to determine current continuation looking at a call/cc invocation? (e.g : Is it a correct strategy to assume that the current continuation is what follows immediately after call/cc closing bracket?)

Answer 1

A continuation is a procedure (in the sense that it's callable and returns true for procedure?), albeit a special one that does not return to the caller of the continuation.

The value(s) you call the continuation with will become the return value(s) of the call/cc invocation that created it.

Example:

> (define $k #f)
> (call-with-values (lambda () (call/cc (lambda (k)
                                          (set! $k k))))
                    (case-lambda (() "Zero values")
                                 ((x) "One value")
                                 ((x y) "Two values")
                                 ((x y z) "Three values")))
"One value"
> (procedure? $k)
#t
> ($k)
"Zero values"
> ($k 1)
"One value"
> ($k 1 2)
"Two values"
> ($k 1 2 3)
"Three values"
> ($k 1 2 3 4)
#<case-lambda-procedure>: arity mismatch;
 the expected number of arguments does not match the given number