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tinmop/src/box.lisp

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Common Lisp
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;; tinmop: an humble gemini and pleroma client
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;; Copyright (C) 2020 cage
;; 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 3 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, see <http://www.gnu.org/licenses/>.
(in-package :box)
(defclass box ()
((contents
:initform nil
:initarg :contents
:accessor contents
:documentation "the thing inside the box"))
(:documentation "A generic object that contains a value"))
(defmethod print-object ((object box) stream)
(print-unreadable-object (object stream :type t)
(format stream "~a" (contents object))))
(defun boxp (thing)
(typep thing 'box))
(defun box (thing)
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"Put `thing' in a box, if thing is a already a box return `thing'."
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(if (boxp thing)
thing
(make-instance 'box :contents thing)))
(defun unbox (thing)
"Unbox `thing' and returns the value contained, if `thing' is not a
box return `thing'."
(if (boxp thing)
(contents thing)
thing))
(defsetf unbox (object) (val)
`(setf (contents ,object) ,val))
(defun dboxp (thing)
"Return non nil id `thing' is a box that contains a box (double box)."
(and (boxp thing)
(boxp (contents thing))))
(defun dbox (thing)
"Box `thing' in a double box."
(if (dboxp thing)
thing
(make-instance 'box :contents (box thing))))
(defun dunbox (object)
"Unbox a double box"
(contents (contents object)))
(defsetf dunbox (object) (val)
`(setf (contents (contents ,object)) ,val))