Why is Python popular, while Lisp and Scheme aren't?

[Pascal Costanza]

Andreas Leitgeb wrote:

> I'd have rewritten it differently (to show the point I was
> trying to make by calling the scheme-snippet ugly):
>   2    if (cardList.size() == 0) return false;
>   3    else if (!cardList.get(0).isVisible()) return false;
>   4    else return ((slotId == 1) || (slotId > 5));
> Now this doesn't make a big difference here, but it makes 
> a lot of a difference, once, things get longer and deeper nested.

I wanted to try the following, so I did. I don't if this would help in 
practice, though... ;)

(defun chained-if (form &key (level 0))
   (cond
    ((symbolp form) form)
    (t (let ((rest (nthcdr 2 form)))
         (cond
          (rest
            (case (first form)
              ('and `(if not ,(second form) then return false
                      else ,@(chained-if (cons 'and rest)
                                         :level level)))
              ('or  `(if ,(second form) then return true
                      else ,@(chained-if (cons 'or rest)
                                         :level level)))))
          ((> level 0)
             `(,(chained-if (second form) :level (1- level))))
          (t
             `(,(second form))))))))

(defun cprint (form)
   (mapc (lambda (elm)
           (when (eq elm 'else) (format t "~%"))
           (format t "~A " elm))
         form))

Now you can do the following.

 > (cprint
    (chained-if
     '(and (not (null card-list))
           (is-visible-p (first card-list))
           (or (= slot-id 1)
               (> slot-id 5)))))
if not (not (null card-list)) then return false
else if not (is-visible-p (first card-list)) then return false
else (or (= slot-id 1) (> slot-id 5))

 > (cprint
    (chained-if
     '(and (not (null card-list))
           (is-visible-p (first card-list))
           (or (= slot-id 1)
               (> slot-id 5)))
     :level 1))
if not (not (null card-list)) then return false
else if not (is-visible-p (first card-list)) then return false
else (if (= slot-id 1) then return true else (> slot-id 5))


All the best,
Pascal

-- 
Pascal Costanza               University of Bonn
mailto:costanza at web.de        Institute of Computer Science III
http://www.pascalcostanza.de  Römerstr. 164, D-53117 Bonn (Germany)