Exercise 3.81
Not sure if this works. Cannot test without rand-update:
1 2 3 4 5 6 7 8 9 10 11 | (define (rand random-stream) (define (random-numbers initial-value) (cons-stream initial-value (stream-map rand-update random-numbers))) (define (dispatch op) (cond ((eq? op 'generate) (random-numbers random-init)) ((eq? op 'reset) (lambda (new-value) (random-numbers (stream-car (stream-filter (lambda (n) (= n new-value)) (random-numbers random-init)))))) (else (error "Operation not found -- RAND" op)))) dispatch) |
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