Solution to 2.33

diff --git a/src/sicp/ex2_33.clj b/src/sicp/ex2_33.clj
new file mode 100644 (file)
index 0000000..57fefcc
--- /dev/null
+++ b/src/sicp/ex2_33.clj
@@ -0,0 +1,36 @@
+(ns sicp.ex2_33
+  (:use [clojure.test]
+        [sicp.ch2-2 :only (accumulate)]))
+
+;; Fill in the missing expressions to complete the
+;; following definitions of some basic list-manipulation
+;; operations as accumulations:
+
+;; (define (map p sequence)
+;;   (accumulate (lambda (x y) <??>) nil sequence))
+(defn mymap [p sequence]
+  (accumulate (fn [x y] (cons (p x) y)) nil sequence))
+
+(deftest test-mymap
+  (is [= (mymap #(* % %) '(1 2 3))
+         '(1 4 9)]))
+
+;; (define (append seq1 seq2)
+;;   (accumulate cons <??> <??>))
+(defn append [seq1 seq2]
+  (accumulate cons seq2 seq1))
+
+(deftest test-append
+  (is [= (append '(1 2 3) '(4 5 6))
+         '(1 2 3 4 5 6)]))
+
+;; (define (length sequence)
+;;   (accumulate <??> 0 sequence))
+(defn length [sequence]
+  (accumulate (fn [x y] (inc y)) 0 sequence))
+
+(deftest test-length
+  (are [x y] [= x y]
+       (length '(1 2 3 4 5)) 5
+       (length '((1 2) 3 4 5) 4)))
+