Exercise 4.28: Eval uses
actual-value rather than eval to evaluate the operator before
passing it to apply, in order to force the value of the operator.  Give
an example that demonstrates the need for this forcing.

Exercise 4.29: Exhibit a program that you would
expect to run much more slowly without memoization than with memoization.
Also, consider the following interaction, where the id procedure is
defined as in Exercise 4.27 and count starts at 0:


(define (square x) (* x x))

;;; L-Eval input:
(square (id 10))

;;; L-Eval value:
⟨response⟩

;;; L-Eval input:
count

;;; L-Eval value:
⟨response⟩

Give the responses both when the evaluator memoizes and when it does not.