#lang racket

;; CSE 413 14au
;; Lecture 7 sample code
;; Hal Perkins

;; return true if x and y have the same shape
(define same-shape
  (lambda (x y)
    (cond ((and (pair? x) (pair? y))
           (and (same-shape (car x) (car y))
                (same-shape (cdr x) (cdr y))))
          ((or (pair? x) (pair? y)) #f)
          (else #t))))

;; (same-shape '(a b c) '(x y z))
;; (same-shape '(a b c) '(a (b c)))
;; (same-shape '(a (b) c) '(w (x) y))


;; given a list of numbers, return a sorted list of those numebers
;; (insertion sort)
(define isort
  (lambda (lst)
    (if (null? lst)
        '()
        (insert (car lst) (isort (cdr lst))))))

;; return copy of lst with x inserted in proper place so result is sorted
(define insert
  (lambda (x lst)
    (cond ((null? lst) (list x))
          ((< x (car lst)) (cons x lst))
          (else (cons (car lst) (insert x (cdr lst)))))))

;; return "n is even" for n >= 0
(define is-it-even?
  (lambda (n)
    (letrec
     ((is-even? (lambda (n)
                  (if (= n 0)
                      #t
                      (is-odd? (- n 1)))))
      (is-odd? (lambda (n)
                 (if (= n 0)
                     #f
                     (is-even? (- n 1))))))
     (is-even? n))))