Square Roots by Newton's Method.

Square Roots by Newton's Method.

(define (sqrt x)
  (define (good-enough? guess)
    (< (abs (- (square guess) x)) 0.001))
  (define (improve guess)
    (average guess (/ x guess)))
  (define (sqrt-iter guess)
    (if (good-enough? guess)
        guess
        (sqrt-iter (improve guess))))
  (sqrt-iter 1.0))

"x" is a free variable in the internal definitions.It gets its value from the argument with which the enclosing procedure sqrt is called.This dicipline is called "lexical scoping".