(servlet (a b)
;; compute area and perimeter of a right triangle
;; with sides of length a and b
 (case a
   ((#null) {Enter ?a=3&b=4 at the end of the URL})
   (else
      {The area of a triangle with sides [a] and [b]
       is [(* a b 0.5)] and the perimeter is
       [(+ a b (sqrt (+ (* a a) (* b b))))]}
    )))