source: trunk/abcl/src/org/armedbear/lisp/cond.lisp

;;; cond.lisp
;;;
;;; Copyright (C) 2004 Peter Graves
;;; $Id: cond.lisp 15569 2022-03-19 12:50:18Z mevenson $
;;;
;;; This program is free software; you can redistribute it and/or
;;; modify it under the terms of the GNU General Public License
;;; as published by the Free Software Foundation; either version 2
;;; of the License, or (at your option) any later version.
;;;
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program; if not, write to the Free Software
;;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
;;;
;;; As a special exception, the copyright holders of this library give you
;;; permission to link this library with independent modules to produce an
;;; executable, regardless of the license terms of these independent
;;; modules, and to copy and distribute the resulting executable under
;;; terms of your choice, provided that you also meet, for each linked
;;; independent module, the terms and conditions of the license of that
;;; module.  An independent module is a module which is not derived from
;;; or based on this library.  If you modify this library, you may extend
;;; this exception to your version of the library, but you are not
;;; obligated to do so.  If you do not wish to do so, delete this
;;; exception statement from your version.

(in-package "SYSTEM")

(defmacro cond (&rest clauses)
  (if (endp clauses)
      nil
      (let ((clause (first clauses)))
        (when (atom clause)
          (error "COND clause is not a list: ~S" clause))
        (let ((test (first clause))
              (forms (rest clause)))
          (if (endp forms)
              (let ((n-result (gensym)))
                `(let ((,n-result ,test))
                   (if ,n-result
                       ,n-result
                       (cond ,@(rest clauses)))))
              `(if ,test
                   (progn ,@forms)
                   (cond ,@(rest clauses))))))))