merry xmas!

xmas.rkt

#! /usr/bin/env racket
#lang racket

(define (color-str n s)
  (~a "\x1b[3" n "m" s "\x1b[0m"))

(define (tree n)
  (append
    (for/list ([r (range 1 (+ n 2) 2)])
      (define not-space
        (if (= 1 r) 
          '("*")
          (for/list ([i (range r)])
            (if (zero? (modulo (+ (* i 3) r) 7)) "o" "l"))))
      (append (make-list (/ (- n r) 2) " ") not-space))
    (list (append (make-list (/ (- n 3) 2) " ") (make-list 3 "b")))))

(define (animate-tree tree base leaf frame)
  (display "\e[1;1H\e[2J")
  (for ([row tree])
    (for ([chr row])
      (display
        (case chr 
          [(" ") " "]
          [("*") (if (even? frame)
            (color-str 3 "*")
            (color-str 3 "`"))]
          [("o") (color-str (random 8) "o")]
          [("l") (color-str 2 leaf)]
          [("b") (color-str 3 base)])))
  (newline))
  (sleep 0.2)
  (animate-tree tree base leaf (add1 frame)))

(define (go n-str base leaf)
  (with-handlers
    ([exn:break?  (lambda (e) 
      (display "\e[1;1H\e[2J")
      (displayln "Merry Xmas!"))])
    (animate-tree
      (tree (string->number n-str)) base leaf 0)))

(apply go (vector->list (current-command-line-arguments)))