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