; 2.1.3
(define (cons x y)
(define (dispatch m)
(cond ((= m 0) x)
((= m 1) y)
(else (error "error"))))
dispatch)
(define (car z) (z 0))
(define (cdr z) (z 1))
티스토리에 소스를 올리는게 넘 불편해서 github repository를 하나 만들었습니다. 앞으로 소스 코드는 여기에 올리는게 어떨지? 이참에 분산 VCS인 git에 대해서도 알아보는건? ^^
커밋을 하려면 github에 가입하고도, 몇 가지 준비가 필요하니 한번 논의해 보시죠.
; ex 2.2
; point
(define (make-point x y) (cons x y))
(define (x-point p) (car p))
(define (y-point p) (cdr p))
(define (point2str p)
(format "(~a,~a)"
(x-point p) (y-point p)))
(define (print-point p)
(newline)
(display (point2str p)))
; segment
(define (make-segment p1 p2) (cons p1 p2))
(define (start-segment s) (car s))
(define (end-segment s) (cdr s))
(define (segment2str s)
(format "~a->~a"
(point2str (start-segment s))
(point2str (end-segment s))))
(define (print-segment s)
(newline)
(display (segment2str s)))
(define (midpoint-segment s)
(define (average a b) (/ (+ a b) 2))
(let ((p1 (start-segment s))
(p2 (end-segment s)))
(make-point (average (x-point p1) (x-point p2))
(average (y-point p1) (y-point p2)))))
; ex 2.3
; rect
(define (make-rect tl-point br-point) (cons tl-point br-point))
;(define (make-rect p1 p2) (cons p1 p2))
(define (top-left-rect r) (car r))
(define (top-right-rect r)
(make-point (x-point (cdr r)) (y-point (car r))))
(define (bottom-left-rect r)
(make-point (x-point (car r)) (y-point (cdr r))))
(define (bottom-right-rect r) (cdr r))
;(define (top-left-rect r)
; (let ((x1 (x-point (car r)))
; (y1 (y-point (car r)))
; (x2 (x-point (cdr r)))
; (y2 (y-point (cdr r))))
; (make-point (min x1 x2) (max y1 y2))))
;(define (top-right-rect r)
; (let ((x1 (x-point (car r)))
; (y1 (y-point (car r)))
; (x2 (x-point (cdr r)))
; (y2 (y-point (cdr r))))
; (make-point (max x1 x2) (max y1 y2))))
;(define (bottom-left-rect r)
; (let ((x1 (x-point (car r)))
; (y1 (y-point (car r)))
; (x2 (x-point (cdr r)))
; (y2 (y-point (cdr r))))
; (make-point (min x1 x2) (min y1 y2))))
;(define (bottom-right-rect r)
; (let ((x1 (x-point (car r)))
; (y1 (y-point (car r)))
; (x2 (x-point (cdr r)))
; (y2 (y-point (cdr r))))
; (make-point (max x1 x2) (min y1 y2))))
(define (rect2str r)
(format "tl=~a\ntr=~a\nbl=~a\nbr=~a"
(top-left-rect r)
(top-right-rect r)
(bottom-left-rect r)
(bottom-right-rect r)))
(define (print-rect r)
(newline)
(display (rect2str r)))
(define (width-rect r)
(- (x-point (top-right-rect r)) (x-point (top-left-rect r))))
(define (height-rect r)
(- (y-point (top-left-rect r)) (y-point (bottom-left-rect r))))
(define (area-rect r)
(* (width-rect r) (height-rect r)))
(define (girth-rect r)
(+ (* (width-rect r) 2) (* (height-rect r) 2)))
