lang racket

;; draw a graph of cos and deriv^3(cos) (require plot) (define ((deriv f) x)

(/ (- (f x) (f (- x 0.001))) 0.001))

(define (thrice f) (lambda (x) (f (f (f x))))) (plot (list (function ((thrice deriv) sin) -5 5)

(function cos -5 5 #:color 'blue)))

;; Print the Greek alphabet (for ([i (in-range 25)])

(displayln
 (integer->char
  (+ i (char->integer #\u3B1)))))

;; An echo server (define listener (tcp-listen 12345)) (let echo-server ()

(define-values (in out) (tcp-accept listener))
(thread (λ ()
           (copy-port in out)
           (close-output-port out)))
(echo-server))