#lang racket

(module drop-on-message racket

(require 2htdp/universe 2htdp/image)

(define (u)

(universe 0

(on-new (lambda (u w) (make-bundle (+ u 1) '() '())))

(on-msg (lambda (u w m) (make-bundle (- u 1) '() (list w))))

(state #t)))

(define (w n)

(big-bang 3

[to-draw (lambda (w) (overlay (text (number->string w) 22 'black) (circle 100 'solid 'red)))]

[on-tick (lambda (w) (if (<= w 1) (make-package 0 n) (- w 1)))]

[register LOCALHOST]

[name n]))

(launch-many-worlds (u) (w "one") (w "two")))

(require (submod "." drop-on-message))

(module drop-bad racket

(require 2htdp/universe 2htdp/image)

(define *world* #false)

(define (u)

(universe '()

(on-new (lambda (u w) (make-bundle (cons w u) '() '())))

(on-msg (lambda (u w m)

;; set *world* to the first world that comes around, reuse

(unless *world* (set! *world* w))

(make-bundle u '() (list *world*))))))

(define (w n)

(big-bang 3

[to-draw (lambda (w) (overlay (text (number->string w) 22 'black) (circle 100 'solid 'red)))]

[on-tick (lambda (w) (if (= w 1) (make-package 0 n) (- w 1)))]

[register LOCALHOST]

[name n]))

(launch-many-worlds (u) (w "one") (w "two") (w "three")))