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Back to Continuations, Continued. On to Continuations, Nearly Concluded.
Held Friday, February 12
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;;; Compute x^n for nonnegative integer n. (define (exp x n) (cond ((= n 0) 1) ((even? n) (lambda (x) (* x x) (exp x (/ n 2)))) ((odd? n) (* x (exp x (- n 1))))))
;;; Compute acc*(x^n) for nonnegative integer n. (define (expacc x n acc) ...)
acc
(since 1*a is a).
((odd? n) (expacc x n (* acc x)))
call/cc
.
(call/cc fun)
calls fun
with the
current continuation.
seta
, that gets the
next value from the list input
> (define (get) (let ((result (car input))) (begin (set! input (cdr input)) result))) > (set! input '(1 2 3)) > (get) 1 > (get) 2 > (get) 3
(- (get) (get))
? (Assuming that
input
is currently (1 2 3)
.)
(get)
first.
We could make that explicit.
> ((lambda (second) (- (get) second)) (get))
(get)
, we
might as well provide one for the first.
> (set! input '(1 2 3)) > ((lambda (b) ((lambda (a) (- a b)) (get))) (get)) 1
(get)
first,
we might write
> (set! input '(1 2 3)) > ((lambda (a) ((lambda (b) (- a b)) (get))) (get)) -1
(define (factorial n) (letrec ((factcps (lambda (n cont) (if (= n 0) (cont 1) (factcps (- n 1) (lambda (subfact) (cont (* n subfact)))))))) (factcps n (lambda (n) n))))
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Back to Continuations, Continued. On to Continuations, Nearly Concluded.
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