Quacking in Racket

quacking.rkt

(define (just-quacking)
  (printf "Quack!\n"))

(define (squeaking)
  (printf "Squeak!\n"))

(define (mute-quacking)
  (printf "<< Silence >>\n"))

(define (quack how-to-quack)
  (how-to-quack))

(quack just-quacking)

(quack squeaking)

(quack mute-quacking)