;;  --------------------------------------------------------------------------
;; |                                                                          |
;; |   FILE           :   reading-v1.rkt                                      |
;; |   AUTHOR         :   Eugene Wallingford                                  |
;; |   CREATION DATE  :   2017/02/16                                          |
;; |                                                                          |
;; |   DESCRIPTION    :   The first version of the procedures defined in      |
;; |                      the reading assignment at the end of Session 12.    |
;; |                      It exposes the implementation details of a          |
;; |                      data abstraction.                                   |
;; |                                                                          |
;; |   REQUIRES       :   No external definitions.  Rackunit for tests.       |
;; |                                                                          |
;;  --------------------------------------------------------------------------

#lang racket
(require rackunit)

;; ---------------------------------------------------------------------------
;; using syntax procedures for a point data type

(define square
  (lambda (x)
    (expt x 2)))

; (define distance
;   (lambda (x y)
;     (sqrt (+ (square (- (car x)
;                         (car y)))
;              (square (- (cdr x)
;                         (cdr y)))))))

(define point->x car)
(define point->y cdr)

(define distance
  (lambda (point1 point2)
    (sqrt (+ (square (- (point->x point1)
                        (point->x point2)))
             (square (- (point->y point1)
                        (point->y point2)))))))

;;  --------------------------------------------------------------------------
;; the "before" picture: code for searching a binary search tree ADT

(define path
  (lambda (n bst)
    (if (null? bst)
        (error 'path "number not found!")
        (if (< n (first bst))
            (cons 'left (path n (second bst)))
            (if (> n (first bst))
                (cons 'right (path n (third bst)))
                '())))))

(define example-tree
   '(14 (7 () (12 () ()))
        (26 (20 (17 () ()) ())
            (31 () ()))))

(check-equal? (path 17 example-tree)
              '(right left left))

;;  --------------------------------------------------------------------------