this was confusing

1 files changed, 28 insertions, 0 deletions

diff --git a/shared/lists.rkt b/shared/lists.rkt
new file mode 100644
index 0000000..9279a57
--- /dev/null
+++ b/shared/lists.rkt
@@ -0,0 +1,28 @@
+#lang racket
+(provide
+  append
+  length
+  list-ref)
+
+(define (append list1 list2)
+  (if (null? list1)
+    list2
+    (cons (car list1) (append (cdr list1) list2))))
+
+(define (length items)
+  (define (length-iter a c)
+    (if (null? a)
+      c
+      (length-iter (cdr a) (+ 1 c))))
+  (length-iter items 0))
+
+(define (list-ref items n)
+  (if (= n 0)
+    (car items)
+    (list-ref 
+      (cdr items) 
+      (- 1 n))))
+(define (last-pair l)
+  (if (null? (cdr l))
+    l
+    (last-pair (cdr l))))