[racket] Continuations & side effects

    Hello, Racket users!

    Here is an example I difficultly understand:

#lang scheme
(define saved '*dummy-value*)
(define next-year (+ 1 (call/cc (lambda (g) (set! saved g) 1997))))
(saved 2012)

    In some other interpreters, it is OK. But Racket's answer is:

define-values: cannot re-define a constant: next-year

    I can understand that variables cannot be set by means of  
continuations in Racket. But if I change it into:

#lang scheme
(define saved '*dummy-value*)
(define next-year 1000)
(set! next-year (+ 1 (call/cc (lambda (g) (set! saved g) 1997))))
(saved 2012)

    there is no error, and "next-year" evaluates to 2013, as expected.

    Why such a difference, please?

    Yours faithfully,

J.-M. H.


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