dcons.lisp

;; Copyright (c) 2011-2012, Krzysztof Drewniak
;; All rights reserved.

;; Redistribution and use in source and binary forms, with or without
;; modification, are permitted provided that the following conditions are met:
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;;       names of its contributors may be used to endorse or promote products
;;       derived from this software without specific prior written permission.

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(in-package #:dlist)

(defstruct dcons 
  "A three-member cons cell for doubly-linked lists, which has `prev', `data' and `next' slots" 
  prev data next)

(defun dcons (prev data next) 
  "Constructs a `dcons' with the given `prev', `data', and `next'"
  (make-dcons :prev prev :data data :next next))

(defun next (dcons)
  "Accesses the `next' slot of a dcons. The `next' of nil is nil." 
  (if dcons (dcons-next dcons)))

(defun prev (dcons) 
  "Accesses the `prev' slot of a dcons. The `prev' of nil is nil."
  (if dcons (dcons-prev dcons)))

(defun data (dcons) 
  "Accesses the `data' slot of a dcons. The `data' of nil is nil."
  (if dcons (dcons-data dcons)))

(defun (setf next) (val place)
  "Sets the `next' slot of `place' (which must be a `dcons') to `val'"
  (setf (dcons-next place) val))

(defun (setf prev) (val place)
  "Sets the `prev' slot of `place' (which must be a `dcons') to `val'"
  (setf (dcons-prev place) val))

(defun (setf data) (val place)
  "Sets the `data' slot of `place' (which must be a `dcons') to `val'"
  (setf (dcons-data place) val))

(declaim (inline dconsp))
(defun dconsp (object)
  "Returns T if `object' is a dcons"
  (typep object 'dcons))