Arbolito de Navidad

arbolito-nav.scm

(cond-expand (chicken (use srfi-1 srfi-13))
             (kawa (require 'srfi-1 'srfi-13)))

(let* ((numeros (filter odd? (iota 20 1)))
       (maxnum  (apply max numeros)))
  (newline)
  (for-each (lambda (n)
              (format #t "~a~a~%" (make-string (/ (- maxnum n) 2) #\space)
                      (make-string n #\*)))
            numeros)
  (do ((i 1 (+ i 1)))
      ((> i 2) (format #t "¡Feliz Navidad y próspero año nuevo 2013!~%"))
    (format #t "~a*~%" (make-string (/ (- maxnum 1) 2) #\space)) ))