sicp-ex-5.3

  
  
 (define sqrt-machine 
   (make-machine 
    '(x guess temp) 
    (list (list '- -) (list '< <) (list '/ /) (list '+ +) (list '* *) (list '> >)) 
    '((assign guess (const 1.0)) 
     test-g 
     (assign temp (op *) (reg guess) (reg guess)) 
     (assign temp (op -) (reg temp) (reg x)) 
     (test (op >) (reg temp) (const 0)) 
     (branch (label iter)) 
     (assign temp (op -) (const 0) (reg temp)) 
     iter 
     (test (op <) (reg temp) (const 0.001)) 
     (branch (label sqrt-done)) 
     (assign temp (op /) (reg x) (reg guess)) 
     (assign temp (op +) (reg temp) (reg guess)) 
     (assign guess (op /) (reg temp) (const 2)) 
     (goto (label test-g)) 
     sqrt-done))) 
 (set-register-contents! sqrt-machine 'x 2) 
 (start sqrt-machine) 
  
 (get-register-contents sqrt-machine 'guess) 
 =>1.4142156862745097