Re: finding the min or max element of a list

(defun best (lst cmp &key (key #'identity))
  (loop with rtn = (car lst)
        for x in (cdr lst)
        when (funcall cmp (funcall key x) (funcall key rtn))
        do (setq rtn x)
        finally (return rtn)))

If one uses a Lispy language, then instead of using
a macro whose source measures 60 kilobytes, he can
simply use the function "reduce".

Gauche Scheme

(define (best lst cmp :key (key identity))
  (reduce
    (lambda (x chosen)
      (if (cmp (key x) (key chosen))  x  chosen))
    #f
    lst))

(best '((a) (f o o b) (b a r) (2 3)) > :key length)
===>
(f o o b)

(best '(5 0 4 9) >)
===>
9

(best '(5 0 4 9) <)
===>
0

(best '() >)
===>
#f

(best '(2) >)
===>
2