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<?xml version="1.0" encoding="ISO-8859-1"?>
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<refentry id="xpf_let">
<refmeta>
<refentrytitle>let</refentrytitle>
<refmiscinfo>XPATH</refmiscinfo>
</refmeta>
<refnamediv>
<refname>let</refname>
<refpurpose>Creates temporary variables and calculates an expression that uses these variables</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis id="xpf_syn_let">
<funcprototype id="xpf_proto_let">
<funcdef>any <function>let</function></funcdef>
<paramdef><parameter>var1name</parameter> string</paramdef>
<paramdef><parameter>var1value</parameter> sequence</paramdef>
<paramdef><parameter>var2name</parameter> string</paramdef>
<paramdef><parameter>var2value</parameter> sequence</paramdef>
<paramdef><parameter>...</parameter></paramdef>
<paramdef><parameter>varNname</parameter> string</paramdef>
<paramdef><parameter>varNvalue</parameter> sequence</paramdef>
<paramdef><parameter>retval</parameter> any</paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 id="xpf_desc_let"><title>Description</title>
<para>
For every pair of arguments, the function calculates values of
these arguments and then creates a new temporary local variable whose name
is the string value of the first argument in pair and the value assigned is
the value of the second argument in pair.
Obviously, the argument for variable name is usually a constant string of
alphanumeric characters.
The expression for a value of variable number I may refer to
variables created during steps 1 to I-1.
When all pairs of arguments are turned into temporary variables,
the last argument is calculated and its value is returned
as the value of the whole expression.
</para>
<para>
Temporary variables are destroyed on return.
</para>
<para>
This function is used in the implementation of
"LET" control operator in XQUERY,
so you will probably use that operator in XQUERY expressions, not the function.
This function may be useful in XPATH expressions and in XSLT stylesheets.
It is not a part of library of standard XQUERY 1.0 functions.
</para>
</refsect1>
<refsect1 id="xpf_params_let"><title>Parameters</title>
<refsect2><title>varIname</title>
<para>Expression for the name for the I-th temporary variable</para></refsect2>
<refsect2><title>varIvalue</title>
<para>Expression for the value for the I-th temporary variable</para></refsect2>
<refsect2><title>retval</title>
<para>Expression for the value to be returned</para></refsect2>
</refsect1>
<refsect1 id="xpf_ret_let"><title>Return Types</title><para>Any, depending on the type of <parameter>retval</parameter> expression.</para></refsect1>
<refsect1 id="xpf_errors_let"><title>Errors</title>
<table><title>Errors signalled by let()</title>
<tgroup cols="4">
<thead><row><entry>SQLState</entry><entry>Error Code</entry><entry>Error Text</entry><entry>Description</entry></row></thead>
<tbody>
<row>
<entry><errorcode>42000</errorcode></entry>
<entry><errorcode>XPF02</errorcode></entry>
<entry><errorname>Wrong number of arguments for XPATH function let(), maybe internal XQuery error</errorname></entry>
<entry>The function should have odd number of arguments: even number of arguments that describe variables plus one for the returned expression.</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1 id="xpf_examples_let"><title>Examples</title>
<example id="xpf_ex_let"><title></title>
<para>These two expressions are equivalent,
but first may be used in any XPATH while second is written in XQUERY syntax</para>
<screen>
let('baseprice', /item/price, 'discount', 0.20, $baseprice * (1.0 - $discount))
LET $baseprice := /item/price, $discount := 0.20 RETURN $baseprice * (1.0 - $discount)
</screen>
</example>
</refsect1>
<refsect1 id="xpf_seealso_let"><title>See Also</title>
<para><link linkend="xpf_for">for()</link></para>
</refsect1>
</refentry>
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