Add net/ricketyspace/sicp/two/two.scm

1 files changed, 43 insertions, 0 deletions

diff --git a/net/ricketyspace/sicp/two/two.scm b/net/ricketyspace/sicp/two/two.scm
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+++ b/net/ricketyspace/sicp/two/two.scm
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+;;;; Under Creative Commons Attribution-ShareAlike 4.0
+;;;; International. See
+;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
+
+(define-module (net ricketyspace sicp two two)
+  #:export (make-point
+            x-point
+            y-point
+            make-segment
+            start-segment
+            end-segment
+            midpoint-segment))
+
+;;; Util
+(define (avg a b)
+  (/ (+ a b) 2.0))
+
+
+;;; Point
+(define (make-point x y)
+  (cons x y))
+
+(define (x-point point)
+  (car point))
+
+(define (y-point point)
+  (cdr point))
+
+;;; Segment
+(define (make-segment start end)
+  (list start end))
+
+(define (start-segment segment)
+  (car segment))
+
+(define (end-segment segment)
+  (cadr segment))
+
+(define (midpoint-segment segment)
+  (make-point (avg (x-point (start-segment segment))
+                   (x-point (end-segment segment)))
+              (avg (y-point (start-segment segment))
+                   (y-point (end-segment segment)))))