Exercise 3.10. In the make-withdraw procedure, the local variable balance is created as a parameter of make-withdraw. We could also create the local state variable explicitly, using let, as follows: (define (make-withdraw initial-amount) (let ((balance initial-amount)) (lambda (amount) (if (>= balance amount) (begin (set! balance (- balance amount)) balance) "Insufficient funds")))) Recall from section 1.3.2 that let is simply syntactic sugar for a procedure call: (let (()) ) is interpreted as an alternate syntax for ((lambda () ) ) Use the environment model to analyze this alternate version of make-withdraw, drawing figures like the ones above to illustrate the interactions (define W1 (make-withdraw 100)) (W1 50) (define W2 (make-withdraw 100)) Show that the two versions of make-withdraw create objects with the same behavior. How do the environment structures differ for the two versions? ———————————————————————————————————————————————————————————————————————— (define (make-withdraw initial-amount) ((lambda (balance) (lambda (amount) ...)) initial-amount)) The difference is that the additional lambda application creates an additional environment structure. The procedure that is bound to W1 has an environment which contains a binding of balance (initially to the value 100). However, this procedure was created in the environment of the outer lambda application, so it points to another environment which contains a binding for initial-amount. Since the body of the procedure which is returned does not reference initial-amount, this difference is not observable.