ARNESI

Messing with numbers 

(define-modify-macro mulf (B)
  *
  "SETF NUM to the result of (* NUM B).")
(define-modify-macro divf (B)
  /
  "SETF NUM to the result of (/ NUM B).")
(define-modify-macro minf (other)
  (lambda (current other)
    (if (< other current)
        other
        current))
  "Sets the place to new-value if new-value is #'< the current value")
(define-modify-macro maxf (other)
  (lambda (current other)
    (if (> other current)
        other
        current))
  "Sets the place to new-value if new-value is #'> the current value")