Function Calls

This page describes how function calls, anonymous functions or high-order function calls are represented in the XPath Model.

Regular Function Calls

A regular function call is represented by a function name and a list of arguments.

XPath:

concat('foo', bar, 'baz')

Model:

<function-call>
   <function name="concat"/>
   <arg>
      <string value="foo"/>
   </arg>
   <arg>
      <locationStep axis="child">
         <nodeTest name="bar" kind="element"/>
      </locationStep>
   </arg>
   <arg>
      <string value="baz"/>
   </arg>
</function-call>

Anonymous Function Definitions

Anonymous functions have no names, but a parameter list. It is modeled with the element function-impl. The function body is defined by a arg element with the role='return'.

XPath:

function($foo){'(' || $foo || ')'}

Model:

<function-impl>
    <param name="foo"/>
    <arg role="return">
       <operation type="concat">
          <arg>
             <string value="("/>
          </arg>
          <concat/>
          <arg>
             <varRef name="foo"/>
          </arg>
          <concat/>
          <arg>
             <string value=")"/>
          </arg>
       </operation>
    </arg>
</function-impl>

Dynamic Function References

Build in functions or functions provided by the host language can be referenced by name and arity.

XPath:

concat#3

Model:

<function name="concat" arity="3"/>

Dynamic Function Calls

One aspect of the high-order function concept is, to call functions dynamically.

XPath:

$foo('arg1', 'arg2', 'arg3')

Model:

<operation type="postfix">
    <arg>
       <varRef name="foo"/>
    </arg>
    <function-call>
       <arg>
          <string value="arg1"/>
       </arg>
       <arg>
          <string value="arg2"/>
       </arg>
       <arg>
          <string value="arg3"/>
       </arg>
    </function-call>
</operation>