Errata for Picturing Programs -- 11

© Stephen Bloch 2010

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-release handler to detect key releases. So to precisely satisfy the statement of the problem, the key handler should actually move 4 pixels left, not 2.