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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: simple loop question
Date: Wed, 4 Sep 2024 00:47:21 -0000 (UTC)
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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
> 
> (let1 y 0 (collect-till x (random 10) (> (inc! y x) 50)))
>   ===>
> (7 9 4 0 6 4 1 3 2 7 0 7 0 1)
> 
> 
> Given:
> 
> (use srfi-27) ;; random-integer
> 
> (define random random-integer)
> 
> (define-syntax collect-till
>   (syntax-rules ()
>     [(collect-till v expr0 expr1)
>      (let ((res '()))
>        (let go ((v expr0))
>          (set! res (cons v res))
>          (if expr1 (reverse res) (go expr0))))]))
> 
> (collect-till x (random 10) (even? x))
>   ===>
> (7 1 6)


Revision:

(collect-till (x (y 0)) (random 10) x (> (inc! y x) 50))

Given:

(define-syntax collect-till
  (syntax-rules ()
    [(collect-till (v (w x) ...) v-val collect test)
     (let ((res '()) (w x) ...)
       (let go ((v v-val))
         (set! res (cons collect res))
         (if test (reverse res) (go v-val))))]
    [(collect-till v v-val collect test)
     (collect-till (v) v-val collect test)]))