Re: Is there a better way to read multiple values from a string

B. Pym wrote:

Pascal J. Bourguignon wrote:
 

I have a strings like "0  2  0  1".  The number of values may vary, but
they all can be read using READ
 
Right now I do the following
(loop
     :for (x pos) = (multiple-value-list
     (read-from-string first-line nil nil :start (or pos 0)))
     :while x
     :collect x)
 
 
Is there a more idiomatic way to read all the tokens in the string and
return them as a list?

 
    (with-input-from-string (in string)
      (loop :for n = (read in nil  nil)
            :while n :collect n))

 
If we are allowed to use a collector, then the loop
becomes much shorter.  Compare:
 
(loop :for n = (read in nil  nil) :while n :collect n))
(until (eof-object? (bag (read))))
 
Gauche Scheme:
 
(define bag (mlistbag))
 
(with-input-from-string "0 4 2 5"
  (lambda()
    (until (eof-object? (bag (read))))))
 
;; Remove the eof-object.
(drop-right (bag) 1)
  ===>
(0 4 2 5)
 
Given:

A better way.


;; Remove the eof-object.
(bag 1 'drop)
  ===>
(0 4 2 5)

Given:

(define (mbag init func :optional (pass-through #f))
  (let ((val init) (func func) (pass-through pass-through))
    (lambda args
      (if (null? args)
        val
        (let ((x (car args)))
          (if (null? (cdr args))
            (begin
              (set! val (func x val))
              (if pass-through
                x
                val))
            (let ((kons (cadr args)))
              (if (or (eq? 'drop kons) (eq? 'DROP kons))
                (do ((n x (- n 1)))
                  ((zero? n)  (if (eq? 'drop kons) (reverse val) val))
                  (set! val (cdr val)))
                (begin
                  (set! val (kons x val))
                  (if pass-through
                    x
                    val))))))))))

(define (mlistbag :optional (raw #f) (pass-through #t))
  (let ((bag (mbag '() cons pass-through)))
    (lambda args
      (if (null? args)
        (if raw
          (bag)
          (reverse (bag)))
        (apply bag args)))))