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From: "B. Pym" <No_spamming@noWhere_7073.org>
Newsgroups: comp.lang.lisp
Subject: Re: Extended loop macro
Date: Fri, 5 Jul 2024 03:40:01 -0000 (UTC)
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Antonio Menezes Leitao wrote:

> Edi Weitz <spamt...@agharta.de> writes: 
> > (loop with scheme-char-seen-p = nil 
> >       for c across string 
> >       when (or (char-not-greaterp #\a c #\z) 
> >                (digit-char-p c) 
> >                (member c '(#\+ #\- #\.) :test #'char=)) 
> >         do (setq scheme-char-seen-p t) 
> >       else return (and scheme-char-seen-p 
> >                        (char= c #\:))) 
> 
> Lot's of extremely nice examples!  And the last one even ends with a 
> smile.  I hope you can see it! 
> 
> Thanks a lot,

In other words, test whether the string begins with a
sequence composed of a-z, 0-9, or [.+-], followed
by ":".

"char-not-greaterp" looks like a joke, doesn't it?
If you think it's Intercal, but it's not, it's
Common Lisp.

The easiest way would be to use regular expressions.
Let's do it a harder way.

Gauche Scheme

(use srfi-13) ;; string functions
(use srfi-14) ;; character sets

(define ch-set
  (char-set-union 
    char-set:lower-case
    char-set:digit
    (string->char-set ".+-")))

(define (foo str)
  (let ((i (string-index str (char-set-complement ch-set)))
        (j (string-index str #\:)))
    (and i j (> i 0) (= i j))))

(foo " hello")
#f

(foo "hello")
#f

(foo ": hello")
#f

(foo "abc: hello")
#t

(foo ".+-: hello")
#t