(       Title:  Double-Linked Nodes
         File:  dnode.fs
      Version:  1.2.3
       Author:  David N. Williams
      License:  LGPL
Last revision:  September 1, 2006
)
\ Copyright (C) 2000-2002, 2006  David N. Williams
(
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or at your option any later version.

This library 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 Lesser General Public License for more details.

Please see the file POLITENESS included with this distribution.

ANS Forth compatible except for:
- Case sensitivity.
- Assumption that zero does not occur as an address.

Please see the file NOTATION.
)

s" undef.fs" INCLUDED  \ ensure [UNDEFINED]

[UNDEFINED] field: [IF]
  : field:  ( offset size -- offset+size )
    create over , +
  DOES>  ( struc -- struc+offset )  @ + ;
[THEN]


\ *** WORDS
(
  Double-linked node structure:
  /DNODE-DATA:  /DNODE-HEADER  >NXNODE  >PREVNODE
)

\ *** DNODE STRUCTURE
(
"Dnodes" are double-linked nodes.  They have two-cell headers,
for a forward and a backward link.  The list words in this
distribution implicitly know the dnode structure; they do not
use the words defined here.

Please see dexample.fs for examples of their use by an
application.
)
  0 ( offset)
  1 cells field:  >nxnode
  1 cells field:  >prevnode
        constant  /dnode-header

: /dnode-data:  ( "name" total.offset -- )  
(
To be used at the end of a data continuation to a double-linked
node structure to define a constant that counts the size of the
data field only, leaving out the header.
)
  /dnode-header - constant ;


\ *** DNODE SPACES
(
A typical use of MAKE-NODES to allocate a space of double-linked
nodes called MYDNODES might be the following:
)
\   ( #nodes /node.data) /dnode-header
\   make-nodes constant mydnodes