math.erl

-module(math).
-compile(export_all).

%% erlang version
pow(_X, 0) ->
  1;
pow(X, N) ->
  X * pow(X, N-1).

%% clojure version

%% non-TCO version
(defn pow
 [x, n]
   (if (= x 0)
       1
       (* x (dec n))))

%% TCO version
(defn pow
 [x, n]
   (loop [n n acc 1]
           (if (= n 0)
               acc
               (recur (dec n) (*' x acc)))))

%% functional version
(defn pow
 [x, n]
   (reduce * (repeat n x)))