Dec. 16, 2010
pp. 129-131: In Worked Exercise 8.4.1, I point out that
whenever a key is typed, it actually causes two keyboard events: one when the key is pressed, and one when it is released.That was true under DrScheme version 4.x, but is no longer true in DrRacket version 5.x; now there's a separate
on-releasehandler to detect key releases. So to precisely satisfy the statement of the problem, the key handler should actually move 4 pixels left, not 2.