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<?xml version="1.0" ?>
<?xml-stylesheet href="api.css" type="text/css" ?>
<!DOCTYPE api SYSTEM "api.dtd" [
]>
<api>
<title>Tree API</title>
<header>
<p>Treeql is a fairly thin query facility over Trees. It implements an ordered set of nodes which are generated and filtered by application of the treeql query language to each node in turn.</p>
<p>Some naming confusion arises because some interesting trees can represent things which have 'attributes', whereas some tree abstractions also provide per-node 'attributes'. We try, in this, to adopt the convention that the abstract tree has 'attributes', whereas the concrete tree may implement node 'properties'.</p>
<p>As treeql iterates over the ordered set of nodes applying query terms to each node in the set - the functionality of treeql is therefore determined by that of the underlying tree.</p>
<p>The main value add of Treeql is that it maintains a node set and handles the distribution of functions over that node set.</p>
<p>Several more abstract 'pre-canned' queries are provided by Treeql, implemented in terms of lower level tree functions.</p>
<p>Some minimal functionality of the underlying tree is assumed by treeql to implement a minimal set of queries deemed necessary.</p>
<p>The underlying tree must provide the following API:</p>
</header>
<group used="$query apply">
<name>Structural generators</name>
<method>
<object><arg>tree</arg></object>
<name>rootname</name>
<args></args>
<result>returns the tree's root</result>
</method>
<method>
<object><arg>tree</arg></object>
<name>children</name>
<args><arg>node</arg></args>
<result>return all immediate children of <arg>node</arg></result>
</method>
<method>
<object><arg>tree</arg></object>
<name>next</name>
<args><arg>node</arg></args>
<result>return next right sibling of <arg>node</arg></result>
</method>
<method>
<object><arg>tree</arg></object>
<name>parent</name>
<args><arg>node</arg></args>
<result>return <arg>node</arg>'s parent</result>
</method>
<method>
<object><arg>tree</arg></object>
<name>previous</name>
<args><arg>node</arg></args>
<result>return left sibling of <arg>node</arg></result>
</method>
</group>
<group used="$query apply">
<name>Property generators</name>
<method>
<object><arg>tree</arg></object>
<name>get</name>
<args><arg>node</arg> <arg>key</arg></args>
<result>get value of property named <arg>key</arg></result>
</method>
<method>
<object><arg>tree</arg></object>
<name>keys</name>
<args><arg>node</arg> <arg>glob</arg></args>
<result>get all <arg>node</arg> property (names,values) whose keys match <arg>glob</arg> (default *)</result>
</method>
<method>
<object><arg>tree</arg></object>
<name>set</name>
<args><arg>node</arg> <arg>prop</arg> <arg>val</arg></args>
<result>set <arg>node</arg> <arg>key</arg> to <arg>value</arg></result>
</method>
</group>
<group used="$query bool">
<name>Predicates</name>
<method>
<object><arg>tree</arg></object>
<name>keyexists</name>
<args><arg>node</arg> <arg>key</arg></args>
<result><arg>node</arg> has property <arg>key</arg></result>
</method>
</group>
</api>
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