From 1b3d763cc69e9635e8f6952ad6ca4f2ae070672e Mon Sep 17 00:00:00 2001
From: Marco <mgross@sw-gross.de>
Date: Tue, 20 Aug 2024 16:45:14 +0200
Subject: [PATCH] sicp exercise 1.4 and various recursive algorithms

---
 exercise1-4.scm             |  5 +++++
 factorial.scm               |  5 +++++
 newton.scm                  | 22 ++++++++++++++++++++++
 test-order-of-execution.scm | 37 +++++++++++++++++++++++++++++++++++++
 4 files changed, 69 insertions(+)
 create mode 100644 exercise1-4.scm
 create mode 100644 factorial.scm
 create mode 100644 newton.scm
 create mode 100644 test-order-of-execution.scm

diff --git a/exercise1-4.scm b/exercise1-4.scm
new file mode 100644
index 0000000..f933d9e
--- /dev/null
+++ b/exercise1-4.scm
@@ -0,0 +1,5 @@
+(define (add-abs a b) 
+  ((if (> b 0) + -) a b )
+  )
+
+(print (add-abs 3 -4))
diff --git a/factorial.scm b/factorial.scm
new file mode 100644
index 0000000..f87da1d
--- /dev/null
+++ b/factorial.scm
@@ -0,0 +1,5 @@
+(define (factorial n)
+  (cond ((= n 2) 2)
+	(else (* (factorial (- n 1)) n))))
+
+(print (factorial 10000))
diff --git a/newton.scm b/newton.scm
new file mode 100644
index 0000000..6d68ea8
--- /dev/null
+++ b/newton.scm
@@ -0,0 +1,22 @@
+(define (sqrt_iter new_guess last_guess x)
+	(if (good_enough? new_guess last_guess)
+	  new_guess
+	  (sqrt_iter (improve new_guess x) new_guess x)
+	)
+)
+
+(define (improve guess x)
+	(/ (+ guess (/ x guess)) 2))
+
+
+(define (good_enough? guess last_guess) 
+  (< (absolute (- guess last_guess)) 0.000000000000001))
+
+(define (absolute x)
+	(if (< x 0)
+	  (- 0 x)
+	  x))
+
+(define (sqrt x) (sqrt_iter (/ x 2.0) x x))
+
+(print (sqrt 2))
diff --git a/test-order-of-execution.scm b/test-order-of-execution.scm
new file mode 100644
index 0000000..a42edba
--- /dev/null
+++ b/test-order-of-execution.scm
@@ -0,0 +1,37 @@
+(define (mainstage-with-if x y) 
+	(print "this is mainstage-with-if")
+	(if (< x y) (stage11 x) (stage21 y)))
+
+(define (mainstage-with-procedure-if x y) 
+	(print "this is mainstage-with-if")
+	(procedure-if (< x y) (stage11 x) (stage21 y)))
+
+(define (stage11 x)
+	(print "this is stage11")
+	(stage12 x))
+
+(define (stage21 x)
+	(print "this is stage21")
+	(stage22 x))
+
+(define (stage12 x)
+	(print "this is stage12")
+	(stage13 x))
+
+(define (stage22 x)
+	(print "this is stage22")
+	(stage23 x))
+
+(define (stage13 x)
+	(print "this is stage13")
+	x)
+
+(define (stage23 x)
+	(print "this is stage23")
+	x)
+
+(define (procedure-if predicate then-clause else-clause)
+  (cond (predicate then-clause) (else else-clause)))
+
+(print (mainstage-with-if 1 2))
+(print (mainstage-with-procedure-if 1 2))