SICP-2.80 solution
;; data-directed version
; generic zero? for all numbers
(define (zero? x) (apply-generic 'zero? x))
; inside scheme-number/rational/complex packages. note that we don't need to tag because the result is boolean
(put 'zero? '(scheme-number)
(lambda (x) (= x 0)))
(put 'zero? '(rational)
(lambda (x) (= (numer x) 0)))
; delegate to lower layer, or we should say, the sub packages
(put 'zero? '(complex) zero?)
; generic zero? for all complex
(define (zero?-complex x) (apply-generic 'zero? x))
; inside polar/rectangular packages. note that we don't need to tag because the result is boolean
(put 'zero? '(polar)
(lambda (z) (= (magnitude z) 0)))
(put 'zero? '(rectangular)
(lambda (z) (and (= (real-part z) 0) (= (imag-part z) 0))))
; generic zero? for all numbers
(define (zero? x) (apply-generic 'zero? x))
; inside scheme-number/rational/complex packages. note that we don't need to tag because the result is boolean
(put 'zero? '(scheme-number)
(lambda (x) (= x 0)))
(put 'zero? '(rational)
(lambda (x) (= (numer x) 0)))
; delegate to lower layer, or we should say, the sub packages
(put 'zero? '(complex) zero?)
; generic zero? for all complex
(define (zero?-complex x) (apply-generic 'zero? x))
; inside polar/rectangular packages. note that we don't need to tag because the result is boolean
(put 'zero? '(polar)
(lambda (z) (= (magnitude z) 0)))
(put 'zero? '(rectangular)
(lambda (z) (and (= (real-part z) 0) (= (imag-part z) 0))))
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