gistfile1.scm

#!/usr/bin/env gsi-script

(define (fact n)
  (let loop ((n n) (r 1))
    (if (< n 2)
      r
      (loop (- n 1) (* r n)))))

(if (not (= (length (command-line)) 2))
  (println "usage: fact1.scm NUMBER")
  (let ((n (string->number (cadr (command-line)))))
    (println (fact n))))