Using a custom function is as easy as eating cheese cake. They can be used like the builtin tags tmpl, sub, var, etc.

01        <patTemplate:tmpl name="page">
02                <div>
03                        Today is
04                        <patTemplate:time format="m/d/Y"/>
05                </div>
06        </patTemplate:tmpl>

This will output Today is [current date]., where [current day] will be replaced with the current date.

01    <patTemplate:tmpl name="root">
02          This is a template that is used to display code.
03          <patTemplate:phpHighlight><?PHP
04                $i = 0;
05                while( $i < 10 )
06                {
07                echo "This is line $i.<br />";
08                $i++;
09                }
10                ?>
11                </patTemplate:phpHighlight>
12    </patTemplate:tmpl>

In the above example, the PHP code enclosed between the <patTemplate:phpHighlight> tags will be syntax highlighted in the output.
Creating a custom Function

Custom Functions have to be placed in patTemplate/Function and extended from patTemplate_Function. You have to implement one method that represents the function:

string patTemplate_Function::call( array params, string content )

The reader will pass an associative array containing all attributes of your tag as well as a string as second parameter, which will contain all character data (and HTML tags) between the opening and closing tags.
In this method you may compute the result and return it as a string. This result will then be inserted in the template instead of your function tag as well as the enclosed content.

You may use all functions, that are located in the patTemplate/Function folder, as patTemplate will auto-load the classes.

Template functions will be evaluated while analyzing the template, there's currently no way to use template variables or any input from the PHP script in the funcitons. Functions may be nested, patTemplate will always evaluate the innermost function first.
Code examples

This example is the code used for the custom function time, which is able to display the current time as well as reformat any timestamp you pass to this.

01        <?PHP
02        /**
03        * patTemplate function that calculates the current time
04        * or any other time and returns it in the specified format.
05        *
06        * @package       patTemplate
07        * @subpackage    Functions
08        * @author        Stephan Schmidt <schst@php.net>
09        */
10        class patTemplate_Function_Time extends patTemplate_Function
11        {
12           /**
13            * name of the function
14            * @access    private
15            * @var       string
16            */
17            var $_name = 'Time';
18       
19           /**
20            * call the function
21            *
22            * @access    public
23            * @param     array    parameters of the function (= attributes of the tag)
24            * @param     string   content of the tag
25            * @return    string   content to insert into the template
26            */
27            function call( $params, $content )
28            {
29                if( !empty( $content ) )
30                {
31                    $params['time'] = $content;
32                }
33               
34                if( isset( $params['time'] ) )
35                {
36                    $params['time'] = strtotime( $params['time'] );
37                }
38                else
39                {
40                    $params['time'] = time();
41                }
42               
43                return date( $params['format'], $params['time'] );
44            }
45        }?>

The next code snippet is all that is needed for the phpHighlight function.

01        <?PHP
02        /**
03        * patTemplate function that highlights PHP code in your templates
04        *
05        * @package        patTemplate
06        * @subpackage    Functions
07        * @author        Stephan Schmidt <schst@php.net>
08        */
09        class patTemplate_Function_Phphighlight extends patTemplate_Function
10        {
11           /**
12            * name of the function
13            * @access    private
14            * @var       string
15            */
16            var $_name = 'Phphighlight';
17       
18           /**
19            * call the function
20            *
21            * @access   public
22            * @param    array    parameters of the function (= attributes of the tag)
23            * @param    string   content of the tag
24            * @return   string   content to insert into the template
25            */
26            function call( $params, $content )
27            {
28                ob_start();
29                highlight_string( $content );
30                $content = ob_get_contents();
31                ob_end_clean();
32                return $content;
33            }
34        }
35        ?>