.. _boolean:

=======
boolean
======= 

The effective boolean value of a sequence

Description
~~~~~~~~~~~
The fn:boolean function calculates the effective boolean value of a sequence. In 
most cases it is unnecessary to call this function because the effective boolean 
value is calculated automatically in many expressions, including conditional and 
logical expressions, where clauses, and predicates.

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   :widths: 40 60
   :header-rows: 1

   * - **Parameters**
     - **Description**
   * - arg:boolean()
     - 

Examples
~~~~~~~~
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   :widths: 50 50
   :header-rows: 1

   * - **XPath**
     - **Results**
   * - boolean( () )
     - false
   * - boolean('')
     - false
   * - boolean(0)
     - false
   * - boolean('0')
     - true
   * - boolean('false')
     - true
   * - boolean(xs:float('NaN'))
     - false
   * - boolean((false(), false(), false()))
     - Error FORG0006
   * - boolean($ordDoc/order[1])
     - true
   * - boolean($ordDoc/noSuchChild)
     - false
   * - boolean(<a>false</a>)
     - true

See Also
~~~~~~~~

.. toctree::
   :titlesonly:
   :glob:

* :ref:`true`.
* :ref:`false`.
* :ref:`not`.
* :ref:`exists`.
* :ref:`empty`.