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))