The textbook uses an optional library named (imaginatively enough) "picturing-programs". Since there have recently been a bunch of version changes beyond my control, here's my advice on how to get things working:
#lang scheme (require (planet sbloch/picturing-programs:1))
exactly like that (the ":1" is important), and hit ENTER. After
between a few seconds and a few minutes, depending on the speed of
your net connection and your computer, you should get a message
saying "Wrote file "picturing-programs.ss" to installed-teachpacks
directory".#lang
scheme should disappear from the definitions pane; if it
doesn't, delete it by hand. Hit the "Run" button near the top right
corner of the DrScheme window.(require installed-teachpacks/picturing-programs) (big-bang (triangle 50 "solid" "blue") (on-tick rotate-cw 1)
(on-draw show-it)) #lang racket (require (planet sbloch/picturing-programs:2))
exactly like that (the ":2" can be left out), and hit ENTER. After
between a few seconds and a few minutes, depending on the speed of
your net connection and your computer, you should get a message
saying "Wrote file "picturing-programs.rkt" to installed-teachpacks
directory".#lang
racket should disappear from the definitions pane; if it
doesn't, delete it by hand. Hit the "Run" button near the top right
corner of the DrRacket window.(require installed-teachpacks/picturing-programs) (big-bang (triangle 50 "solid" "blue") (on-tick rotate-cw 1)
(on-draw show-it))