From 9fa67213bfe13f0fe63bcbdc1fbc93f220861b0d Mon Sep 17 00:00:00 2001
From: Tobias Eidelpes <tobias@eidelpes.info>
Date: Fri, 4 Nov 2022 18:38:25 +0100
Subject: [PATCH] Initial commit

---
 .gitignore    | 43 ++++++++++++++++++++++++++++++++++++++
 chapter2.lisp | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 chapter2.lisp

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..45f2085
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,43 @@
+*~
+\#*\#
+/.emacs.desktop
+/.emacs.desktop.lock
+*.elc
+auto-save-list
+tramp
+.\#*
+
+# flymake-mode
+*_flymake.*
+
+# eshell files
+/eshell/history
+/eshell/lastdir
+
+# elpa packages
+/elpa/
+
+# reftex files
+*.rel
+
+# AUCTeX auto folder
+/auto/
+
+# cask packages
+.cask/
+dist/
+
+# Flycheck
+flycheck_*.el
+
+# server auth directory
+/server/
+
+# projectiles files
+.projectile
+
+# directory configuration
+.dir-locals.el
+
+# network security
+/network-security.data
diff --git a/chapter2.lisp b/chapter2.lisp
new file mode 100644
index 0000000..f43bac0
--- /dev/null
+++ b/chapter2.lisp
@@ -0,0 +1,58 @@
+(defun add-rat (x y)
+  (make-rat (+ (* (numer x) (denom y))
+	       (* (numer y) (denom x)))
+	    (* (denom x) (denom y))))
+
+(defun sub-rat (x y)
+  (make-rat (- (* (numer x) (denom y))
+	       (* (numer y) (denom x)))
+	    (* (denom x) (denom y))))
+
+(defun mul-rat (x y)
+  (make-rat (* (numer x) (numer y))
+	    (* (denom x) (denom y))))
+
+(defun div-rat (x y)
+  (make-rat (* (numer x) (denom y))
+	    (* (numer y) (denom x))))
+
+(defun equal-ratp (x y)
+  (= (* (numer x) (denom y))
+     (* (numer y) (denom x))))
+
+(defun make-rat (n d)
+  (let ((g (gcd n d)))
+    (cons (/ n g) (/ d g))))
+
+(defun numer (x) (car x))
+(defun denom (x) (cdr x))
+
+(defun print-rat (x)
+  (format t "~a/" (numer x))
+  (format t "~a~%" (denom x)))
+
+;; Exercise 2.2
+(defun make-segment (start end)
+  (cons
+   (make-point (x-point start) (y-point start))
+   (make-point (x-point end) (y-point end))))
+
+(defun start-segment (segment) (car segment))
+(defun end-segment (segment) (cdr segment))
+
+(defun average (x y)
+  (/ (+ x y) 2))
+(defun midpoint-segment (segment)
+  (make-point (average (x-point (start-segment segment))
+		       (x-point (end-segment segment)))
+	      (average (y-point (start-segment segment))
+		       (y-point (end-segment segment)))))
+
+(defun make-point (x y)
+  (cons x y))
+
+(defun x-point (point) (car point))
+(defun y-point (point) (cdr point))
+
+(defun print-point (p)
+  (format t "(~a,~a)~%" (x-point p) (y-point p)))