(define testcond
  (lambda (l)
    (cond
     ((assq 'a l) => (lambda (p) (set-car! p 'd)))
     ((assq 'b l) extra-sym => (lambda (p) (set-car! p 'e)))
     ((assq 'c l) => (lambda (p) (set-car! p 'f))))))
