sicp-ex-2.79

 ;; ----------------------------------------------- 
 ;; EXERCISE 2.79 
 ;; ----------------------------------------------- 
  
 (define (install-scheme-number-package) 
   ;; ... 
   (put 'equ? '(scheme-number scheme-number) =) 
   'done) 
  
 (define (install-rational-package) 
   ;; ... 
   (define (equ? x y) 
     (= (* (numer x) (denom y)) (* (numer y) (denom x)))) 
   ;; ... 
   (put 'equ? '(rational rational) 
        (lambda (x y) (tag (equ? x y)))) 
   'done) 
  
 (define (install-complex-package) 
   ;; ... 
   (define (equ? x y) 
     (and (= (real-part x) (real-part y)) (= (imag-part x) (imag-part y)))) 
   ;; ... 
   (put 'equ? '(complex complex) 
        (lambda (x y) (tag (equ? x y)))) 
   'done) 
  
 (define (equ? x y) (apply-generic 'equ? x y)) 

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