Exercise 5.5.  Hand-simulate the factorial and Fibonacci machines, using 
some nontrivial input (requiring execution of at least one recursive 
call). Show the contents of the stack at each significant point in the 
execution.

————————————————————————————————————————————————————————————————————————

The Fibonacci machine:

 0. (controller
 1.   (assign continue (label fib-done))
 2. fib-loop
 3.   (test (op <) (reg n) (const 2))
 4.   (branch (label immediate-answer))
 5.   ;; set up to compute Fib(n - 1)
 6.   (save continue)
 7.   (assign continue (label afterfib-n-1))
 8.   (save n)                           ; save old value of n
 9.   (assign n (op -) (reg n) (const 1)); clobber n to n - 1
10.   (goto (label fib-loop))            ; perform recursive call
11. afterfib-n-1                         ; upon return, val contains Fib(n - 1)
12.   (restore n)
13.   (restore continue)
14.   ;; set up to compute Fib(n - 2)
15.   (assign n (op -) (reg n) (const 2))
16.   (save continue)
17.   (assign continue (label afterfib-n-2))
18.   (save val)                         ; save Fib(n - 1)
19.   (goto (label fib-loop))
20. afterfib-n-2                         ; upon return, val contains Fib(n - 2)
21.   (assign n (reg val))               ; n now contains Fib(n - 2)
22.   (restore val)                      ; val now contains Fib(n - 1)
23.   (restore continue)
24.   (assign val                        ;  Fib(n - 1) +  Fib(n - 2)
25.           (op +) (reg val) (reg n)) 
26.   (goto (reg continue))              ; return to caller, answer is in val
27. immediate-answer
28.   (assign val (reg n))               ; base case:  Fib(n) = n
29.   (goto (reg continue))
30. fib-done)

We begin with the value 2 in register n.
n=2
on line 0, and the stack is empty:
0 ()
1 cont=fib-done
6 (fib-done)
7 cont=afterfib-n-1
8 (fib-done 2)
9 n=1
3 n<2 is true
28 val=1
29 goto afterfib-n-1
12 n=2
12 (fib-done)
13 cont=fib-done
13 ()
15 n=0
16 (fib-done)
17 cont=afterfib-n-2
18 (fib-done 1)
19 goto 3, test is true, goto 27
28 val=0
29 goto afterfib-n-2
21 n=0
22 val=1
22 (fib-done)
23 cont=fib-done
23 ()
24 val=1
26 goto fib-done
So we are left with 1 in val, which is indeed the second Fibonacci number.

Factorial example would be very similar, skipping.