(load "ch2support.scm")

(define pi (* 4 (atan 1)))
;;; POINT
(define (make-point x y)
  (define (dispatch op)
    (cond ((eq? op 'x) x)
	  ((eq? op 'y) y)
	  ((eq? op 'distance) (lambda (p)
				(sqrt (+ (square (- (p 'x) x)) (square (- (p 'y) y))))))
	  ((eq? op 'print) (display "(")(display x)(display ",")(display y)(display ")") #t) 
	  (else (error "Unknown op --- MAKE-POINT" op) nil)))
  dispatch)
;;; POINT EXAMPLES
(define p1 (make-point 0 0))
(define p1.5 (make-point 0 1))
(define p2 (make-point 1 1))
(define p3 (make-point 1 0))

((p2 'distance) p1)
(p3 'print)


;;;; POLYGON
(define (make-polygon attributes) ; attributes are the # vertices, followed by that many points
  (define (dispatch op)
    (let ((other-vertices (cddr attributes)); list of second point onwards
	  (first-vertex (cadr attributes)) ; first point, save to close the perimeter
	  (sides (car attributes)) ; number of sides
	  (vertices (cdr attributes)))
      (define (add-perimeter result rest-vertices counter)
	(if (= counter sides)(+ result ((first-vertex 'distance) (car rest-vertices)))
	    (add-perimeter (+ result (((car rest-vertices) 'distance) (cadr rest-vertices)))
			   (cdr rest-vertices)
			   (1+ counter)))) ; end of add-perimeter
      (cond ((eq? op 'perimeter) (add-perimeter 0 vertices 1))
	    ((eq? op 'print) (newline) (for-each (lambda (x) (newline) (x 'print)) vertices) #t)
	    (else (error "Unknown op --- MAKE-POLYGON" op)))))
  dispatch)
;; POLYGON EXAMPLES			       
(define pol1 (make-polygon (list 3 p1 p2 p3))) ;; a triangle
(pol1 'perimeter)
(pol1 'print)
(define pol2 (make-polygon (list 4 p1 p1.5 p2 p3))) ; a square
(pol2 'perimeter)
(pol2 'print)

;;;; CIRCLE
(define (make-circle attributes) ; attributes are the center and radius
  (define (dispatch op)
    (let ((center (car attributes))
	  (radius (cadr attributes)))
      (cond ((eq? op 'perimeter) (* 2 pi radius))
	    ((eq? op 'print) (newline)(display "center: ")(center 'print)
			       (newline)(display "radius: ")(display radius) #t)
	    ((eq? op 'radius) radius)
	    ((eq? op 'center) center)
	    (else (error "Unknown op --- MAKE-CIRCLE" op)))))
  dispatch)

(define cir1 (make-circle (list p1 2)))
(cir1 'print)
(cir1 'perimeter)

;;;; GENERIC FIGURE HANDLER
(define (generic-figure-handler figure op)
  (figure op))

(generic-figure-handler pol1 'print)
(generic-figure-handler cir1 'perimeter)
(generic-figure-handler pol1 'perimeter)