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racketcontinuations

How do I know whether an expression is a continuation?

(+ 2 (let/cc cont
    (begin
     (set! global-cont cont)
     3)))
5

global-cont
#<continuation>

(global-cont 5) ; global-cont: (+ 2 _)
7

I know the whole block (+ 2 ... 3))) is a continuation. But why global-cont is a continuation also? I tried to check the let/cc document, but it's hard to understand.

Solution

  • In this expression:

    (let/cc cont body ...)

    cont is a continuation (+ 2 _), and in the body you're doing this:

    (set! global-cont cont)

    So basically you're assigning cont to global-cont, making it also a continuation.