added day three

daythree.rkt

@@ -0,0 +1,44 @@
+#lang racket
+
+(define (square x)
+	(* x x))
+
+;; more obfuscated functions, please
+(define (head x) (car x))
+(define (tail x) (cdr x))
+
+(define (foldr func arr val)
+	(if (null? arr)
+		val
+		(foldl func (cdr arr) (func (car arr) val))))
+
+; (define (foldr func arr val)
+; 	(if (null? arr)
+; 		val
+; 		(foldr func (cdr arr) (func val (car arr)))))
+
+;; won't work because there's no difference between 0-10-5-1 and 0-1-5-10
+; (define (foldr-cheating func arr starting-value) (foldl func (reverse arr) starting-value))
+
+
+;; not working yet
+; (define (foldr-helper func old-arr new-value)
+; 	(if (null? old-arr)
+; 		new-value
+
+; (define (foldr func arr starting-value)
+; 	(foldr-helper func arr (list starting-value)))
+; (println "(foldl - '(10 5 1) 0)")
+(foldr - '(10 5) 0)
+
+;; not sure if there is a preferred way to do this
+(define (fib n) 
+	(if (< n 1)
+		0
+		(if (= n 1)
+			1
+			(+ (fib (- n 1)) (fib (- n 2))))))
+
+(println "fib(0-10)")
+(for ([i (in-range 10)])
+    (println (fib i)))