Implement variable hooks

class.templater.php

@@ -15,6 +15,7 @@ if($_CPHP !== true) { die(); }
 
 $template_cache = array();
 $template_global_vars = array();
+$template_variable_hooks = array();
 
 define("MODE_NONE", 0);
 define("MODE_TAG", 1);
@@ -444,6 +445,14 @@ class NewTemplater
 	{
 		return $this->root->Evaluate($localized_strings, $data);
 	}
+	
+	public static function RegisterVariableHook($name, $function)
+	{
+		global $template_variable_hooks;
+		$template_variable_hooks[$name] = $function;
+		
+		return true;
+	}
 }
 
 class TemplateElement
@@ -491,6 +500,8 @@ class TemplateElement
 	
 	public function FetchVariable($variable_name, $data)
 	{
+		global $template_variable_hooks;
+		
 		$operation = null;
 		
 		if(strpos($variable_name, "|") !== false)
@@ -511,6 +522,26 @@ class TemplateElement
 			
 			$target = $this->parent;
 			
+			if(isset($template_variable_hooks[$collection_name]))
+			{
+				$function = $template_variable_hooks[$collection_name];
+				
+				if(is_null($operation))
+				{
+					return $function(true, $key_name);
+				}
+				elseif($operation == "isset")
+				{
+					return true;
+				}
+				elseif($operation == "isempty")
+				{
+					$result = $function(false, $key_name);
+					return empty($result);
+				}
+			}
+			else
+			{
 				/* Traverse up the tree to find the provider of this particular collection */
 				while(true)
 				{
@@ -555,12 +586,31 @@ class TemplateElement
 					}
 				}
 			}
+		}
 		else
 		{
 			/* Stand-alone variable. */
 			$target = $this->parent;
 			
-			if(isset($data[$variable_name]))
+			if(isset($template_variable_hooks[$variable_name]))
+			{
+				$function = $template_variable_hooks[$variable_name];
+				
+				if(is_null($operation))
+				{
+					return $function(true);
+				}
+				elseif($operation == "isset")
+				{
+					return true;
+				}
+				elseif($operation == "isempty")
+				{
+					$result = $function(false);
+					return empty($result);
+				}
+			}
+			elseif(isset($data[$variable_name]))
 			{
 				if(is_null($operation))
 				{