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<h1 class="content-header header-section1" id="ref_directive_visit" itemprop="headline">visit, recurse, fallback</h1>
</div></div><div class="page-menu">
<div class="page-menu-title">Page Contents</div>
<ul><li><a class="page-menu-link" href="#autoid_130" data-menu-target="autoid_130">Synopsis</a></li><li><a class="page-menu-link" href="#autoid_131" data-menu-target="autoid_131">Description</a><ul><li><a class="page-menu-link" href="#autoid_132" data-menu-target="autoid_132">Visit</a></li><li><a class="page-menu-link" href="#autoid_133" data-menu-target="autoid_133">Recurse</a></li><li><a class="page-menu-link" href="#autoid_134" data-menu-target="autoid_134">Fallback</a></li></ul></li></ul> </div><a name="ref.directive.visit"></a>
<h2 class="content-header header-section2" id="autoid_130">Synopsis</h2>
<pre class="metaTemplate"><code class="inline-code">&lt;#visit <em class="code-color">node</em> using <em class="code-color">namespace</em>&gt;</code>
or
<code class="inline-code">&lt;#visit <em class="code-color">node</em>&gt;</code></pre>
<pre class="metaTemplate"><code class="inline-code">&lt;#recurse <em class="code-color">node</em> using <em class="code-color">namespace</em>&gt;</code>
or
<code class="inline-code">&lt;#recurse <em class="code-color">node</em>&gt;</code>
or
<code class="inline-code">&lt;#recurse using <em class="code-color">namespace</em>&gt;</code>
or
<code class="inline-code">&lt;#recurse&gt;</code></pre>
<pre class="metaTemplate"><code class="inline-code">&lt;#fallback&gt;</code></pre>
<p>Where:</p>
<ul>
<li>
<code class="inline-code"><em class="code-color">node</em></code>:
Expression evaluates to a <a href="xgui_expose_dom.html">node
variable</a>.
</li>
<li>
<code class="inline-code"><em class="code-color">namespace</em></code>: A
<a href="dgui_misc_namespace.html">namespace</a>, or a
sequence of namespaces. A namespace can be given with the
namespace hash (a.k.a. gate hash), or with a string literal that
store the path of template that could be imported. Instead of
namespace hashes, you can use plain hashes as well.
</li>
</ul>
<h2 class="content-header header-section2" id="autoid_131">Description</h2>
<p>The <code class="inline-code">visit</code> and <code class="inline-code">recurse</code>
directives are used for the recursive processing of trees. In
practice, this will mostly be used for <a href="xgui.html">processing XML.</a></p>
<h3 class="content-header header-section3" id="autoid_132">Visit</h3>
<p>When you call <code class="inline-code">&lt;#visit
<em class="code-color">node</em>&gt;</code>, it looks for a
user-defined directive (like a macro) to invoke that has the name
deducted from the node&#39;s name
(<code class="inline-code"><em class="code-color">node</em>?node_name</code>) and
namespace
(<code class="inline-code"><em class="code-color">node</em>?node_namespace</code>).
The rules of name deduction:</p>
<ul>
<li>
<p>If the node doesn&#39;t support node namespaces (as text
nodes in XML), then the directive name is simply the name of
the node
(<code class="inline-code"><em class="code-color">node</em>?node_name</code>).
<span class="marked-for-programmers">A node does not support node
namespaces if the <code class="inline-code">getNodeNamespace</code> method
returns <code class="inline-code">null</code>.</span></p>
</li>
<li>
<p>If the node does support node namespaces (as element
nodes in XML), then a prefix deduced from the node namespace
maybe appended before the node name with a colon used as
separator (e.g. <code class="inline-code">e:book</code>). The prefix, and if
there is a prefix used at all, depends on what prefixes has
been registered with the <code class="inline-code">ns_prefixes</code>
parameter of the <code class="inline-code">ftl</code> directive in the <a href="dgui_misc_namespace.html">FTL namespace</a> where
<code class="inline-code">visit</code> looks for the handler directive
(which is not necessary the same as the FTL namespace where
<code class="inline-code">visit</code> was called from, as you will see
later). Concretely, if there was no default namespace
registered with <code class="inline-code">ns_prefixes</code> then for nodes
that does not belong to any namespace (<span class="marked-for-programmers">when <code class="inline-code">getNodeNamespace</code>
returns <code class="inline-code">&quot;&quot;</code></span>) no prefix is used. If
there was a default namespace registered with
<code class="inline-code">ns_prefixes</code> then for nodes that does not
belong to any namespace prefix <code class="inline-code">N</code> is used,
and for nodes that belong to the default node namespace no
prefix is used. Otherwise, in both case, the prefix associated
to the node namespace with the <code class="inline-code">ns_prefixes</code>
is used. If there is not prefix associated to the node
namespace of the node, then <code class="inline-code">visit</code> simply
behave as if there was no directive found with the proper
name.</p>
</li>
</ul>
<p>The node for which the user-defined directive was invoked is
available for it as special variable <code class="inline-code">.node</code>.
Example:</p>
<div class="code-block role-template">
<div class="code-block-label">Template</div><pre class="code-block-body">&lt;#-- Assume that nodeWithNameX?node_name is &quot;x&quot; --&gt;
&lt;#visit nodeWithNameX&gt;
Done.
&lt;#macro x&gt;
Now I&#39;m handling a node that has the name &quot;x&quot;.
Just to show how to access this node: this node has ${.node?children?size} children.
&lt;/#macro&gt;</pre> </div>
<p>The output will be something like:</p>
<div class="code-block role-output">
<div class="code-block-label">Output</div><pre class="code-block-body"> Now I&#39;m handling a node that has the name &quot;x&quot;.
Just to show how to access this node: this node has 3 children.
Done.</pre> </div>
<p>If one or more namespaces is specified using the optional
<code class="inline-code">using</code> clause, then <code class="inline-code">visit</code>
will look for the directives in those namespaces only, with the
earlier specified namespaces in the list getting priority. If no
<code class="inline-code">using</code> clause is specified, the namespace or
sequence of namespaces specified with the <code class="inline-code">using</code>
clause of the last uncompleted <code class="inline-code">visit</code> call is
reused. If there is no such pending <code class="inline-code">visit</code> call,
then the current namespace is used. For example, if you execute
this template:</p>
<div class="code-block role-template">
<div class="code-block-label">Template</div><pre class="code-block-body">&lt;#import &quot;n1.ftl&quot; as n1&gt;
&lt;#import &quot;n2.ftl&quot; as n2&gt;
&lt;#-- This will call n2.x (because there is no n1.x): --&gt;
&lt;#visit nodeWithNameX using [n1, n2]&gt;
&lt;#-- This will call the x of the current namespace: --&gt;
&lt;#visit nodeWithNameX&gt;
&lt;#macro x&gt;
Simply x
&lt;/#macro&gt;</pre> </div>
<p>and this is <code class="inline-code">n1.ftl</code>:</p>
<div class="code-block role-template">
<div class="code-block-label">Template</div><pre class="code-block-body">&lt;#macro y&gt;
n1.y
&lt;/#macro&gt;</pre> </div>
<p>and this is <code class="inline-code">n2.ftl</code>:</p>
<div class="code-block role-template">
<div class="code-block-label">Template</div><pre class="code-block-body">&lt;#macro x&gt;
n2.x
&lt;#-- This callc n1.y as it inherits the &quot;using [n1, n2]&quot; from the pending visit call: --&gt;
&lt;#visit nodeWithNameY&gt;
&lt;#-- This will call n2.y: --&gt;
&lt;#visit nodeWithNameY using .namespace&gt;
&lt;/#macro&gt;
&lt;#macro y&gt;
n2.y
&lt;/#macro&gt;</pre> </div>
<p>then this will print:</p>
<div class="code-block role-output">
<div class="code-block-label">Output</div><pre class="code-block-body">
n2.x
n1.y
n2.y
Simply x
</pre> </div>
<p>If <code class="inline-code">visit</code> doesn&#39;t find a user-defined
directive in either FTL namespaces with the name identical to the
name deduced with the rules described earlier, then it tries to
find an user-defined directive with name
<code class="inline-code">@<em class="code-color">node_type</em></code>, or if
the node does not support node type property (i.e.
<code class="inline-code"><em class="code-color">node</em>?node_type</code>
returns undefined variable), then with name
<code class="inline-code">@default</code>. For the lookup, it uses the same
mechanism as was explained earlier. If it still doesn&#39;t find an
user-defined directive to handle the node, then
<code class="inline-code">visit</code> stops template processing with error.
Some XML specific node types have special handling in this regard;
see: <a href="xgui_declarative_details.html">XML Processing Guide/Declarative XML processing/Details</a>. Example:</p>
<div class="code-block role-template">
<div class="code-block-label">Template</div><pre class="code-block-body">&lt;#-- Assume that nodeWithNameX?node_name is &quot;x&quot; --&gt;
&lt;#visit nodeWithNameX&gt;
&lt;#-- Assume that nodeWithNameY?node_type is &quot;foo&quot; --&gt;
&lt;#visit nodeWithNameY&gt;
&lt;#macro x&gt;
Handling node x
&lt;/#macro&gt;
&lt;#macro @foo&gt;
There was no specific handler for node ${node?node_name}
&lt;/#macro&gt;</pre> </div>
<p>This would print:</p>
<div class="code-block role-output">
<div class="code-block-label">Output</div><pre class="code-block-body">Handling node x
There was no specific handler for node y
</pre> </div>
<h3 class="content-header header-section3" id="autoid_133">Recurse</h3>
<a name="ref.directive.recurse"></a>
<p>The <code class="inline-code">&lt;#recurse&gt;</code> directive is really
syntactic sugar. It visits all children nodes of the node (and not
the node itself). So, to write:</p>
<div class="code-block role-template">
<div class="code-block-label">Template</div><pre class="code-block-body">&lt;#recurse <em>someNode</em> using <em>someLib</em>&gt;</pre> </div>
<p>is equivalent to writing:</p>
<div class="code-block role-template">
<div class="code-block-label">Template</div><pre class="code-block-body">&lt;#list <em>someNode</em>?children as <em>child</em>&gt;&lt;#visit <em>child</em> using <em>someLib</em>&gt;&lt;/#list&gt;</pre> </div>
<p>However, target node is optional in the
<code class="inline-code">recurse</code> directive. If the target node is
unspecified, it simply uses the <code class="inline-code">.node</code>. Thus,
the terse instruction <code class="inline-code">&lt;#recurse&gt;</code> is
equivalent to:</p>
<div class="code-block role-template">
<div class="code-block-label">Template</div><pre class="code-block-body">&lt;#list .node?children as child&gt;&lt;#visit child&gt;&lt;/#list&gt;</pre> </div>
<p>As a side comment for those who are familiar with XSLT,
<code class="inline-code">&lt;#recurse&gt;</code> is pretty much exactly
analogous to the <code class="inline-code">&lt;xsl:apply-templates/&gt;</code>
instruction in XSLT.</p>
<h3 class="content-header header-section3" id="autoid_134">Fallback</h3>
<a name="ref.directive.fallback"></a>
<p>As you could learn earlier, in the documentation of the
<code class="inline-code">visit</code> directive, the user-defined directive
that handles the node is maybe searched in multiple FTL
name-spaces. The <code class="inline-code">fallback</code> directive can be used
in a user-defined directive that was invoked to handle a node. It
directs FreeMarker to continue the searching for the user-defined
directive in the further name-spaces (that is, in the name-spaces
that are after the name-space of the currently invoked
user-defined directive in the list of name-spaces). If a handler
for the node is found then it is invoked, otherwise
<code class="inline-code">fallback</code> does nothing.</p>
<p>A typical usage of this to write customization layer over a
handler library, that sometimes passes the handling to the
customized library:</p>
<div class="code-block role-template">
<div class="code-block-label">Template</div><pre class="code-block-body">&lt;#import &quot;/lib/docbook.ftl&quot; as docbook&gt;
&lt;#--
We use the docbook library, but we override some handlers
in this namespace.
--&gt;
&lt;#visit document using [.namespace, docbook]&gt;
&lt;#--
Override the &quot;programlisting&quot; handler, but only in the case if
its &quot;role&quot; attribute is &quot;java&quot;
--&gt;
&lt;#macro programlisting&gt;
&lt;#if .node.@role[0]!&quot;&quot; == &quot;java&quot;&gt;
&lt;#-- Do something special here... --&gt;
...
&lt;#else&gt;
&lt;#-- Just use the original (overidden) handler --&gt;
&lt;#fallback&gt;
&lt;/#if&gt;
&lt;/#macro&gt;</pre> </div>
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