LFE SICP square root first example

sqrt.lfe

(defmodule sqrt
  (export (sqrt 1)))

(defun sqrt [x]
  (sqrt (* 0.5 x)
        x))

(defun sqrt [guess x]
  (if (good-enough? guess x)
      guess
      (sqrt (improve guess x)
            x)))

(defun good-enough? [guess x]
  (< (absv (- (square guess)
              x))
     0.0001))

(defun improve [guess x]
  (average guess
           (/ x guess)))

(defun average [x y]
  (/ (+ x y)
     2))

(defun absv
  ([x] (when (< x 0))
   (- x))
  ([x]
   x))

(defun square [x]
  (* x x))