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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp
Subject: Re: Macro noob
Date: Wed, 18 Jun 2025 17:56:30 -0000 (UTC)
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B. Pym wrote:

> Frank Buss wrote:
> 
> > (defun count-words (string)
> >   "returns the number of words in a string"
> >   (loop for char across string
> >         with count = 0 and in-word = nil
> >         finally (return count)
> >         do (if (alphanumericp char)
> >                (unless in-word
> >                  (setf in-word t)
> >                  (incf count))
> >              (setf in-word nil))))
> 
> Gauche Scheme:
> 
> (use srfi-13) ;; string-index string-skip
> (use srfi-14) ;; character sets
> 
> (define (count-words str)
>   (define p 0)  ;; Position.
>   (let go ((cnt 0) (inc-a 1) (inc-b 0)
>            (f0 string-index) (f1 string-skip))
>     (set! p (f0 str char-set:letter+digit p))
>     (if p
>       (go (+ cnt inc-a) inc-b inc-a f1 f0)
>       cnt)))
> 
> gosh> (count-words "hi ?? ho xx23zz")
> 3
> gosh> (count-words " !!  ")
> 0
> gosh> (count-words "   ")
> 0
> gosh> (count-words "  foo---bar  ")
> 2

More understanbable.

(define (count-words str)
  (define p 0)  ;; Position.
  (let go ((cnt 0)
           (inc-a 1) ;; Amount to increment cnt when finding alphanumerics.
           (inc-b 0) ;; Amount to increment cnt when skipping alphanumerics.
           (func-a string-index) ;; Function to find an alphanumeric.
           (func-b string-skip)) ;; Function to skip alphanumerics.
    (set! p (func-a str char-set:letter+digit p))
    (if p
      ;; When we recurse, we swap the increments and the
      ;; functions.  So if we were finding alphanumerics,
      ;; during the next pass we'll be skipping alphanumerics.
      (go (+ cnt inc-a) inc-b inc-a func-b func-a)
      cnt)))