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<h1>saxon:assign</h1>
<p>The <code>saxon:assign</code> instruction is used to change the value of a global variable that
has previously been declared using <code>xsl:variable</code> (or <code>xsl:param</code>).
The variable or parameter
must be marked as assignable by including the extra attribute
<code>saxon:assignable="yes"</code></p>
<p><i>This instruction works only with global variables. It should be regarded as
deprecated, and may be withdrawn completely at some time in the future, since it is incompatible with many
of the optimizations that Saxon now performs.</i></p>
<p><i>A better approach to the problem of updateable variables, based on the theory of monads in the
functional programming literature, has been described by Dimitre Novatchev in section 3.6 of his paper
<a href="http://www.mulberrytech.com/Extreme/Proceedings/html/2003/Novatchev01/EML2003Novatchev01.html"
class="bodylink">Functional programming in XSLT using the FXSL library</a>.
This approach does not require any XSLT extensions, and the constructs it uses are implemented efficiently
in Saxon.</i></p>
<p>As with <code>xsl:variable</code>, the name of the variable is given in the mandatory <b>name</b> attribute,
and the new value may be given either by an expression in the <code>select</code> attribute, or by expanding
the content of the <code>xsl:assign</code> element.</p>
<p>If the <code>xsl:variable</code> element has an <code>as</code> attribute, then the value is converted
to the required type of the variable in the usual way.</p>
<p>Example:</p>
<div class="codeblock"
style="border: solid thin; background-color: #B1CCC7; padding: 2px">
<pre>
<code>
<xsl:variable name="i" select="0" saxon:assignable="yes"/>
<xsl:template name="loop">
<saxon:while test="$i &lt; 10">
The value of i is <xsl:value-of select="$i"/>
<saxon:assign name="i" select="$i+1"/>
</saxon:while>
</xsl:template>
</code>
</pre>
</div>
<p>The <code>saxon:assign</code> element itself does not allow an <code>as</code> attribute. Instead,
it calculates the value of the variable as if <code>as="item()*"</code> were specified. This means that
the result of the construct:</p>
<div class="codeblock"
style="border: solid thin; background-color: #B1CCC7; padding: 2px">
<pre>
<code><saxon:assign name="a">London</saxon:assign></code>
</pre>
</div>
<p>is a single text node, not a document node containing a text node. If you want to create a document
node, use <code>xsl:document</code>.</p>
<p><b>Note:</b> Using <code>saxon:assign</code> is cheating. XSLT is designed as
a language that is free of side-effects, which is why variables are not assignable.
Once assignment to variables is allowed, certain optimizations become impossible.
At present this doesn't affect Saxon, which generally executes the stylesheet
sequentially. However, there are some circumstances in which the order of execution
may not be quite what you expect, in which case <code>saxon:assign</code> may show
anomalous behavior. In principle the <code>saxon:assignable</code> attribute is designed
to stop Saxon doing optimizations that cause such anomalies, but you can't always rely
on this.</p>
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