examples/scripts/fact

   1 #! /usr/local/bin/guile -s
   2 !#
   3 ;;; Commentary:
   4
   5 ;;; This is a command-line factorial calculator.  Run like this:
   6 ;;;
   7 ;;; ./fact 5
   8 ;;;
   9 ;;; to calculate the factorial of 5
  10
  11 ;;; Author: Martin Grabmueller
  12 ;;; Date: 2001-05-29
  13
  14 ;;; Code:
  15
  16 (use-modules (ice-9 getopt-long))
  17
  18 ;; This is the grammar for the command line synopsis we expect.
  19 ;;
  20 (define command-synopsis
  21   '((version (single-char #\v) (value #f))
  22     (help    (single-char #\h) (value #f))))
  23
  24 ;; Display version information and exit.
  25 ;;
  26 (define (display-version)
  27   (display "fact 0.0.1\n"))
  28
  29 ;; Display the usage help message and exit.
  30 ;;
  31 (define (display-help)
  32   (display "Usage: fact [options...] number\n")
  33   (display "  --help, -h           Show this usage information\n")
  34   (display "  --version, -v        Show version information\n"))
  35
  36 ;; Interpret options, if --help or --version was given, print out the
  37 ;; requested information and exit.  Otherwise, calculate the factorial
  38 ;; of the argument.
  39 ;;
  40 (define (main options)
  41   (let ((help-wanted (option-ref options 'help #f))
  42         (version-wanted (option-ref options 'version #f))
  43         (args (option-ref options '() '())))
  44     (cond
  45       ((or version-wanted help-wanted)
  46        (if version-wanted
  47          (display-version))
  48        (if help-wanted
  49          (display-help)))
  50       ((not (= (length args) 1))
  51        (display-help))
  52       (else
  53        (display (fact (string->number (car args))))
  54        (newline)))))
  55
  56 ;; Calculate the factorial of n.
  57 ;;
  58 (define (fact n)
  59   (if (< n 2)
  60     1
  61     (* n (fact (- n 1)))))
  62
  63 ;; Call the main program with parsed command line options.
  64 ;;
  65 (main (getopt-long (command-line) command-synopsis))
  66
  67 ;; Local variables:
  68 ;; mode: scheme
  69 ;; End: