a recursive process
evaluating (factorial 3)
- (factorial 3)
- (* 3 (factorial 2))
- (* 3 (* 2 (factorial 1)))
- (* 3 (* 2 1))
- (* 3 2)
- 6
observe
- process grows and then shrinks
- defers work to be done later: the chain of *’s
- number of steps and length of deferred computation are both proportional to k when computing (factorial k), so called a ‘linear recursive process’