1 files changed, 57 insertions, 0 deletions
diff --git a/ex/2/47.rkt b/ex/2/47.rkt
new file mode 100644
index 0000000..1d2abd3
--- /dev/null
+++ b/ex/2/47.rkt
@@ -0,0 +1,57 @@
+;;;; License: CC0-1.0
+
+#lang racket
+
+(provide make-frame
+         make-frame-alt)
+
+(require "46.rkt")
+
+
+;;; frame functions
+
+(define  (make-frame origin edge1 edge2)
+  (list origin edge1 edge2))
+
+(define (origin-frame frame)
+  (car frame))
+
+(define (edge1-frame frame)
+  (car (cdr frame)))
+
+(define (edge2-frame frame)
+  (car (cdr (cdr frame))))
+
+
+;;; alternative frame functions
+
+(define (make-frame-alt origin edge1 edge2)
+  (cons origin (cons edge1 edge2)))
+
+(define (origin-frame-alt frame)
+  (car frame))
+
+(define (edge1-frame-alt frame)
+  (car (cdr frame)))
+
+(define (edge2-frame-alt frame)
+  (cdr (cdr frame)))
+
+;;; tests
+
+(module+ tests
+  (require rackunit)
+
+  (define f1 (make-frame (make-vect 1 2) (make-vect 3 4) (make-vect 5 6)))
+  (define f2 (make-frame-alt (make-vect 1 2) (make-vect 3 4) (make-vect 5 6)))
+
+  ;; test selectors for make-frame
+  (check-equal? (origin-frame f1) '(1 . 2))
+  (check-equal? (edge1-frame f1)  '(3 . 4))
+  (check-equal? (edge2-frame f1)  '(5 . 6))
+
+  ;; test selectors for make-frame-alt
+  (check-equal? (origin-frame-alt f2) '(1 . 2))
+  (check-equal? (edge1-frame-alt f2)  '(3 . 4))
+  (check-equal? (edge2-frame-alt f2)  '(5 . 6))
+  "all tests ran")