a simple big-bang program that plays notes depending on the x-position of the mouse

mouse-tone-player.rkt

(require 2htdp/image)
(require 2htdp/universe)
(require rsound)

;; a world is an integer.
;; rep. the "x" position of the mouse

(define SCREENWIDTH 400)

;; draw the world
(define (draw-world st)
  (rectangle SCREENWIDTH 100 "solid" "purple"))

;; should draw a blank rectangle
;(draw-world 1)

;; take two things, return the second
(define (both a b)
  b)

;; map an x position to a midi note number
;; from 0 to 127
(define (x-to-note-num st)
  (* 127 (/ st 550)))

;; should play a note
(define (play-it st)
  (both (play (synth-note "vgame" 49 (x-to-note-num st) 22010))
        st))

(check-expect (play-it 3) 3)

;; given a state, an x and y coordinate, and a mouse event,
;; return the x coordinate (the new state)
(define (mousehandler st x y ev)
  x)

;; start the world
(big-bang 0
          [on-mouse mousehandler]
          [on-tick play-it 1/4]
          [to-draw draw-world])