Sam对《The Little Schemer (4/e)》的笔记(2)

Continuation passing style:

(define evens*-co
  (lambda (xs col)
    (cond [(null? xs) (col '() 1 0)]
          [(atom? (car xs))
           (if (even? (car xs))
               (evens*-co
                (cdr xs)
                (lambda (xss p s)
                  (col
                   (cons (car xs) xss)
                   (* (car xs) p)
                   s)))
               (evens*-co
                (cdr xs)
                (lambda (xss p s)
                  (col xss p (+ (car xs) s)))))]
          [else (evens*-co
                 (car xs)
                 (lambda (al ap as)
                   (evens*-co
                    (cdr xs)
                    (lambda (dl dp ds)
                      (col
                       (append al dl)
                       (* ap dp)
                       (+ as ds))))))])))

图灵的停机问题的证明

(define eternity
  (lambda (x) (eternity x)))

(define last-try
  (lambda (x)
    (and (will-stop? last-try)
         (eternity x))))