Pascal Bourguignon spam at thalassa.informatimago.com
Thu Oct 9 18:30:21 EDT 2003

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"Andrew Dalke" <adalke at mindspring.com> writes:

> Pascal Costanza:
> > So what's the result of ("one" - "two") then? ;)
> 
> It's undefined on strings -- a type error.  Having + doesn't
> mean that - must exist.

What about:

(defun nl-string-to-number (text)
  ;; Of course, you could program it more intelligently and more efficiently.
  (do* ((i 0                   (1+ i))
        (s (format nil "~r" i) (format nil "~r" i))
        )
      ((or (string-equal s text) (< (* 2 (length text)) (length s)))
       (when (string-equal s text) i)))
  );;nl-string-to-number

(defmacro def-s-op (name num-op)
  `(defun ,name (&rest args)
     (format nil "~r"
             (apply (function ,num-op)
                    (mapcar (function nl-string-to-number) args))))
  );;def-s-op


(def-s-op +s  +)
(def-s-op -s  -)
(def-s-op *s  *)
(def-s-op /s  /)
(def-s-op =s  =)
(def-s-op /=s /=)
(def-s-op <s  <)
(def-s-op <=s <=)
(def-s-op >s  >)
(def-s-op =>s <=)

(-s "one" "two")

==> "minus one"


-- 
__Pascal_Bourguignon__
http://www.informatimago.com/
Do not adjust your mind, there is a fault in reality.

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