SICP Lecture 01

A simple example to show essential scheme syntax.

(define (abs x)
  (if (< x 0)
      (- x)
      x))

(define (square x) (* x x))

(define (average x y) (/ (+ x y) 2))

(define (sqrt x)
  (define (improve guess) (average guess (/ x guess)))
  (define (good-enough? guess) (< (abs (- (square guess) x)) 0.001))
  (define (try guess)
    (if (good-enough? guess)
        guess
        (try (improve guess))))
  (try 1))