(require 'stdlib)

(define (smooth f dx)
  "return the average value of f over the interval 2*dx around some x"
  (lambda (x)
    (/ (+ (f (- x dx)) (f x) (f (+ x dx))) 3)))

(define (f x)
  (sin x))

(define f-smooth-0.5 (smooth f 0.5))

(define (f-smooth x)
  (f-smooth-0.5 x))

(let ((x 0))
  (while (< x 3.14)
    (printf "%s %s %s\n" x (f x) (f-smooth x))
    (setq x (+ x 0.1))))