| Title: Symbol Node
Description: None
Copyright (c) 2000 Steven J. Metsker.
Copyright (c) 2001 The Open For Business Project - www.ofbiz.org
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the "Software"),
to deal in the Software without restriction, including without limitation
the rights to use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT
OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
THE USE OR OTHER DEALINGS IN THE SOFTWARE.
A SymbolNode object is a member of a tree that
contains all possible prefixes of allowable symbols. Multi-
character symbols appear in a SymbolNode tree
with one node for each character.
For example, the symbol =:~ will appear in a
tree as three nodes. The first node contains an equals sign,
and has a child; that child contains a colon and has a
child; this third child contains a tilde, and has no
children of its own. If the colon node had another child
for a dollar sign character, then the tree would contain
the symbol =:$.
A tree of SymbolNode objects collaborate to
read a (potentially multi-character) symbol from an input
stream. A root node with no character of its own finds an
initial node that represents the first character in the
input. This node looks to see if the next character in the
stream matches one of its children. If so, the node
delegates its reading task to its child. This approach
walks down the tree, pulling symbols from the input that
match the path down the tree.
When a node does not have a child that matches the next
character, we will have read the longest possible symbol
prefix. This prefix may or may not be a valid symbol.
Consider a tree that has had =:~ added and has
not had =: added. In this tree, of the three
nodes that contain =:~, only the first and
third contain complete symbols. If, say, the input contains
=:a, the colon node will not have a child that
matches the 'a' and so it will stop reading. The colon node
has to "unread": it must push back its character, and ask
its parent to unread. Unreading continues until it reaches
an ancestor that represents a valid symbol.
author:
Steven J. Metsker
version:
1.0 |
