foo.php

<?php

class MyTemplateProvider implements TemplateGlobalProvider {

	/**
	 * @return array
	 */
	public static function get_template_global_variables() {
		return array(
			'CurrentURL' => 'get_current_url'
		);
	}

	/**
	 * @return string
	 */
	public function get_current_url() {
		return Controller::curr()->request->getURL(true);
	}

}

// dev/build, then use in template with {$CurrentURL}