Promises and Racket's dialects

Dear Racket users,

 Within the documentation or elsewhere on Internet, is there a survey about the different ways of implementing promises in Racket and its dialects. I know that there are several ways, especially about recursive promises, but I am puzzled. For example:

(define x 0)

(define p
 (delay (if (= x 5)
 x
 (begin
 (set! x (+ x 1)) (force p) (set! x (+ x 1)) x))))

If I understood, Racket does not allow such recursive promise.

In #!r5rs (force p) => 5

In #!r7rs (force p) => 10 and then (force p) => 5, what is surprising because "force" is supposed to yield the same result for the same promise.

 Please is there a place where these differences are discussed? Many thanks in advance,

J.-M. Hufflen

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