How to do exponentiation in clojure?

clojure exponentiation
Peter picture Peter · Feb 20, 2011 · Viewed 45.9k times · Source

How can I do exponentiation in clojure? For now I'm only needing integer exponentiation, but the question goes for fractions too.

Answer

John Lawrence Aspden picture John Lawrence Aspden · Feb 20, 2011

classic recursion (watch this, it blows stack)

(defn exp [x n]
     (if (zero? n) 1
         (* x (exp x (dec n)))))

tail recursion 

(defn exp [x n]
  (loop [acc 1 n n]
    (if (zero? n) acc
        (recur (* x acc) (dec n)))))

functional

(defn exp [x n]
  (reduce * (repeat n x)))

sneaky (also blows stack, but not so easily)

(defn exp-s [x n]
  (let [square (fn[x] (* x x))]
    (cond (zero? n) 1
          (even? n) (square (exp-s x (/ n 2)))
          :else (* x (exp-s x (dec n))))))

library

(require 'clojure.contrib.math)

Related questions

Scala vs. Groovy vs. Clojure

Can someone please explain the major differences between Scala, Groovy and Clojure. I know each of these compiles to run on the JVM but I'd like a simple comparison between them.

Read More
A regex to match a substring that isn't followed by a certain other substring

I need a regex that will match blahfooblah but not blahfoobarblah I want it to match only foo and everything around foo, as long as it isn't followed by bar. I tried using this: foo.*(?<!bar) which is fairly …

Read More
How to bundle a native library and a JNI library inside a JAR?

The library in question is Tokyo Cabinet. I want is to have the native library, JNI library, and all Java API classes in one JAR file to avoid redistribution headaches. There seems to be an attempt at this at GitHub, …

Read More