1 Quick Start

This program is in a language that has been enriched with Javascript-specific functions. It can be partially evaluated in plain Racket, but evaluation will halt at the call to image-url because image-url constructs a image DOM element and needs to run in an Javascript context.

Once the program is saved, create a new file called "run.rkt" in the same working directory with the following contents:

#lang racket

(require (planet dyoo/js-vm:1:7))

(run-in-browser "test.rkt")

When this program is executed, run-in-browser will take "test.rkt" and translate it to run on the browser; a temporary web-server will opened and your browser’s window will open with the running program.

Finally, you can create zip packages by using create-zip-package. For example, modify "run.rkt" to be:

#lang racket

(require dyoo/js-vm:1:7)

(create-zip-package "test.rkt" "test.zip")

A slightly more substantial example is an animation using a built-in functional event-driven programming library.

#lang planet dyoo/js-vm:1:7

; falling.ball.rkt

; Simple falling ball example. A red ball falls down the screen

; until hitting the bottom.

(define-struct world (radius y))

; The dimensions of the screen:

(define WIDTH 320)

(define HEIGHT 480)

; The radius of the red circle.

(define RADIUS 15)

; The world is the distance from the top of the screen.

(define INITIAL-WORLD (make-world RADIUS 0))

; tick: world -> world

; Moves the ball down.

(define (tick w)

(make-world RADIUS (+ (world-y w) 5)))

; hits-floor?: world -> boolean

; Returns true when the distance reaches the screen height.

(define (hits-floor? w)

(>= (world-y w) HEIGHT))

; We have some simple test cases.

(check-expect (hits-floor? (make-world RADIUS 0)) false)

(check-expect (hits-floor? (make-world RADIUS HEIGHT)) true)

; render: world -> scene

; Produces a scene with the circle at a height described by the world.

(define (render w)

(place-image (circle RADIUS "solid" "red") (/ WIDTH 2) (world-y w)

(empty-scene WIDTH HEIGHT)))

; Start up a big bang, 15 frames a second.

(check-expect (big-bang INITIAL-WORLD

(on-tick tick 1/15)

(to-draw render)

(stop-when hits-floor?))

(make-world 15 480))