Re: simple loop question

B. Pym wrote:

Lars Brinkhoff wrote:
 

use LOOP to collect random integers into a list until the sum of that
list exceeds a constant (say 50).

 
(loop for x = (random 10) collect x sum x into y until (> y 50))

 
Gauche Scheme

If we are allowed to set up a couple of collectors, the
solution is tiny.  Comparing it to the LOOP version:


(until (> (s (c (random 10))) 50)) (c)
(loop for x = (random 10) collect x sum x into y until (> y 50))


Here's the code:

(use srfi-27) ;; random-integer
(define random random-integer)

(let ((c (mlistbag)) (s (mbag 0 +)))
  (until (> (s (c (random 10))) 50))
  (c))

  ===>
(8 1 9 8 1 9 9 2 6)


Given:

(define (mbag init func :optional (pass-through #f))
  (let ((val init) (func func) (pass-through pass-through))
    (lambda args
      (if (null? args)
        val
        (begin
          (set! val
            ;; A "kons" may have been supplied.
            ((if (null? (cdr args)) func (cadr args))
              (car args) val))
          (if pass-through
            (car args)
            val))))))
(define (mlistbag :optional (pass-through #t))
  (let ((bag (mbag '() cons pass-through)))
    (lambda args
      (if (null? args)
        (reverse (bag))
        (apply bag args)))))