start ch2

1 files changed, 45 insertions, 0 deletions

diff --git a/coding-exercises/2/7.rkt b/coding-exercises/2/7.rkt
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+++ b/coding-exercises/2/7.rkt
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+#lang racket
+(provide
+  make-interval
+  upper-bound
+  lower-bound
+  add-interval
+  mul-interval
+  div-interval
+  print-interval)
+
+(define (add-interval x y)
+  (make-interval (+ (lower-bound x) (lower-bound y))
+                 (+ (upper-bound x) (upper-bound y))))
+
+(define (mul-interval x y)
+  (let ((p1 (* (lower-bound x) (lower-bound y)))
+        (p2 (* (lower-bound x) (upper-bound y)))
+        (p3 (* (upper-bound x) (lower-bound y)))
+        (p4 (* (upper-bound x) (upper-bound y))))
+    (make-interval (min p1 p2 p3 p4)
+                   (max p1 p2 p3 p4))))
+
+(define (div-interval x y)
+  (mul-interval x
+                (make-interval (/ 1.0 (upper-bound y))
+                               (/ 1.0 (lower-bound y)))))
+
+(define (make-interval a b) (cons a b))
+(define (lower-bound x) (car x))
+(define (upper-bound x) (cdr x))
+
+(define (print-interval x)
+  (newline)
+  (display "interval{")
+  (display (lower-bound x))
+  (display ",")
+  (display (upper-bound x))
+  (display "}")
+  (newline))
+
+(define (print)
+  (define test-interval (make-interval 1 2))
+  (print-interval test-interval))
+
+(print)