Added iterate function and tests

Author: oholiab

pixie/stdlib.pxi

@@ -3072,3 +3072,11 @@ ex: (vary-meta x assoc :foo 42)"
             (swap! cache assoc argsv ret)
             ret)
           val)))))
+
+(defn iterate
+  {:doc "Returns a lazy sequence of x, (f x), (f (f x)) etc. f must be free of
+    side-effects"
+   :signatures [[f x]]
+   :added "0.1"}
+  [f x]
+  (lazy-seq (cons x (iterate f (f x)))))

tests/pixie/tests/test-stdlib.pxi

@@ -761,3 +761,7 @@
 (t/deftest test-memoize
   (let [f (memoize rand)]
     (t/assert= (f) (f))))
+
+(t/deftest test-iterate
+  (t/assert= (take 5 (iterate inc 5)) '(5 6 7 8 9))
+  (t/assert= (str (type (iterate inc 1))) "<type pixie.stdlib.LazySeq>"))