*
* RUN-TIME SYSTEM
*
  0:     LD  5,1(0) ; read command-line arg into r5, the funcall arg slot
  1:    LDA  6,1(7) ; store return address in r6
  2:    LDA  7,5(0) ; branch to MAIN, at [r0]+5
  3:    OUT  4,0,0  ; print value in r4, the funcall return slot
  4:   HALT  0,0,0 
*
* MAIN
*
  5:    MUL  5,5,5  ; compute result
  6:    ADD  4,0,5  ; store return value from r5 into r4
  7:    LDA  7,0(6) ; store return address in r7, for branch back