| #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)) |
