My first scheme program, after watching the first HP SICP class video - June 28, 2011

sqrt.scm

(define (sqrt2 x)
  (define (square num)
    (* num num))
  (define (average a1 a2)
    (/ (+ a1 a2) 2))
  (define (improve guess)
    (average guess (/ x guess)))
  (define (good-enough? guess)
    (< (abs (- (square guess) x))
       .000000001))
  (define (try guess)
    (if (good-enough? guess)
        guess
        (try (improve guess))))
  (try 1))