From Newsgroup: comp.lang.lisp

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:

(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)))))

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From Newsgroup: comp.lang.lisp

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)))))
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