light_template.php

<?php

// FROM: http://stackoverflow.com/a/6319265
function renderString($str, $parms)
{
    // if
    $str = preg_replace_callback('/{{if (?P<name>\w+)}}(?P<inner>.*?){{endif}}/is', function($match) use ($parms) {
        if( isset($parms[$match['name']])) {
            // recursive
            return renderString($match['inner'], $parms);
        }
    }, $str);
    // loop
    $str = preg_replace_callback('/{{loop (?P<name>\w+)}}(?P<inner>.*?){{endloop}}/is', function($match) use ($parms) {
        if( isset($parms[$match['name']]) && is_array($parms[$match['name']])) {
            $str = '';
            foreach ($parms[$match['name']] as $value) {
                $parms['loop'] = $value;
                // recursive
                $str .= renderString($match['inner'], $parms);
            }
            return $str;
        }
    }, $str);
    // var
    $str = preg_replace_callback('/{{(?P<name>\w+)}}/is', function($match) use ($parms) {
        if( isset($parms[$match['name']])) {
            return htmlspecialchars($parms[$match['name']]);
        }
    }, $str);
    return $str;
}

$template = "<h1>{{title}}</h1>

{{if optional}}
<p>Optional: {{optional}}</p>
{{endif}}

{{if noop}}I'm not there{{endif}}

<ul>
{{loop numbers}}
<li>{{symbol}} {{loop}}</li>
{{endloop}}
</ul>";

echo renderString($template, array(
    'title'    => 'The Title',
    'optional' => 'I am optional',
    'numbers'  => array( 'one', 'two', 'three'),
    'symbol'   => '>',
));