The deposit and withdraw procedures in the make-account code from SICP both have seemingly useless balance variable expression to evaluate,

1. What is the practical purpose for doing that? (To me it seems redundant peace of code, but I don’t think Abelson and Sussman would put something useless).

2. Meanwhile, in DrRacket [run from IDE], the balance from withdraw gets printed, whereas the balance from deposit does not. Why is that? Is it a DrRacket’s thing, a bug, or what.

3. In Chicken Scheme and MIT Scheme [run from command line], the balance is not printed consistently for both deposit and withdraw.

The code is below. I just added (display “deposit:n”) and (display “withdraw:n”) to the original code for convenience.
The balance variable expression in question is right after the display expressions, on the same line of code.

#lang racket

(define (make-account balance)
  (define (withdraw amount)
    (if (>= balance amount)
        (begin (set! balance (- balance amount))
               (display "withdraw:n") balance)
        "Insufficient funds"))
  (define (deposit amount)
    (set! balance (+ balance amount))
    (display "deposit:n") balance)
  (define (dispatch m)
    (cond ((eq? m 'deposit) deposit)
          ((eq? m 'withdraw) withdraw)
          ((eq? m 'balance) balance)
          (else
           (error "Unknown request: MAKE-ACCOUNT" m))))
  dispatch)

(define (exchange account1 account2)
  (let ((difference (- (account1 'balance)
                       (account2 'balance))))
    ((account1 'withdraw) difference)
    ((account2 'deposit) difference)))


(define a1 (make-account 100))
(define a2 (make-account 75))

(exchange a1 a2)

E.g., here is the output from Dr.Racket,

withdraw:
deposit:
100

withdraw prints nothing, deposit prints ‘100’. Why not to print either both or none?