started with section 2.2

diff --git a/src/sicp/ch2_2.clj b/src/sicp/ch2_2.clj
new file mode 100644 (file)
index 0000000..7af5040
--- /dev/null
+++ b/src/sicp/ch2_2.clj
@@ -0,0 +1,62 @@
+(ns sicp.ch2_2)
+
+(cons 1
+      (cons 2
+           (cons 3
+                 (cons 4 nil))))
+;;=> (1 2 3 4)
+(list 1 2 3 4)
+
+(def one-thru-four (list 1 2 3 4))
+;;=> #'user/one-thru-four
+(first one-thru-four)
+;;=> 1
+(rest one-thru-four)
+;;=> (2 3 4)
+(cons 10 one-thru-four)
+;;=> (10 1 2 3 4)
+(cons 5 one-thru-four)
+;;=> (5 1 2 3 4)
+
+;; get nth element of a list
+(defn list-ref [items n]
+  (if (= n 0)
+    (first items)
+    (list-ref (rest items) (- n 1))))
+
+(list-ref one-thru-four 3)
+;;=> 4
+(list-ref one-thru-four 5)
+;;=> nil
+(list-ref one-thru-four 1)
+;;=> 2
+(list-ref one-thru-four 0)
+;;=> 1
+
+(defn length [items]
+  (if (empty? items)
+    0
+    (+ 1 (length (rest items)))))
+
+(length one-thru-four)
+;;=> 4
+
+(defn- length-i [items n]
+  (if (empty? items)
+    n
+    (length-i (rest items) (+ 1 n))))
+
+(defn length-iter [items]
+  (length-i items 0))
+
+(length-iter one-thru-four)
+;;=> 4
+
+(defn append [list1 list2]
+  (if (empty? list1)
+    list2
+    (cons (first list1)
+         (append (rest list1) list2))))
+
+(append one-thru-four one-thru-four)
+;;=> (1 2 3 4 1 2 3 4)
\ No newline at end of file