Variable 1 — assignment (4:48)
PLAI§8.2. Back to variables and assignment, instead of boxes.
Variable 2 — interp (2:21)
Implementing interp for variables. See variable.rkt.
Variable 3 — variables as boxes (4:47)
On the expressiveness of variables and boxes. (They’re about the same.)
Variable 4 — call by reference (4:12)
An aside about a generally bad idea.