sicp-2-5-2
Posted on 2015-02-25 07:03:37 +0900 in SICP
2.81
If try to coerce two numbers, it would fall into a infinite loop.
It would show an error message if trying to convert an augument to its own type, which is correct.
2.82
(define (apply-generic op . args)
(define (apply-generic op args type-list)
(if (null? type-list)
(error "No method for types"
(list op (map type-tag args))))
(let ((new-args (map (lambda (x)
(convert x (car type-list)))
args)))
(let ((new-tags (map type-tag new-args)))
(let ((proc (get op new-tags)))
(if proc
(apply proc (map contents new-args))
(apply-generic op args (cdr type-list)))))))
(let ((type-tags (map type-tag args)))
(let ((proc (get op type-tags)))
(if proc
(apply proc (map contents args))
(apply-generic op args type-tags)))))2.83
(define (raise x) (apply-generic 'raise x))
(put 'raise 'integer
(lambda (x) (make-rational x 1)))
(put 'raise 'rational
(lambda (x) (make-real (/ (numer x) (denom x)))))
(put 'raise 'real
(lambda (x) (make-from-real-imag x 0)))2.84 ~ 2.97
I decided to skip the above ones just because they are so code intense, maybe I will come back to them in the future.
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