added filter to apply dynamic filter

Sources/Extension.swift

@@ -26,6 +26,10 @@ open class Extension {
 
   /// Registers a template filter with the given name
   public func registerFilter(_ name: String, filter: @escaping (Any?, [Any?]) throws -> Any?) {
+    filters[name] = .arguments({ value, args, _ in try filter(value, args) })
+  }
+
+  public func registerFilter(_ name: String, filter: @escaping (Any?, [Any?], Context) throws -> Any?) {
     filters[name] = .arguments(filter)
   }
 }
@@ -59,28 +63,28 @@ class DefaultExtension: Extension {
     registerFilter("join", filter: joinFilter)
     registerFilter("split", filter: splitFilter)
     registerFilter("indent", filter: indentFilter)
+    registerFilter("filter", filter: filterFilter)
   }
 }
 
 
 protocol FilterType {
-  func invoke(value: Any?, arguments: [Any?]) throws -> Any?
+  func invoke(value: Any?, arguments: [Any?], context: Context) throws -> Any?
 }
 
 enum Filter: FilterType {
   case simple(((Any?) throws -> Any?))
-  case arguments(((Any?, [Any?]) throws -> Any?))
+  case arguments(((Any?, [Any?], Context) throws -> Any?))
 
-  func invoke(value: Any?, arguments: [Any?]) throws -> Any? {
+  func invoke(value: Any?, arguments: [Any?], context: Context) throws -> Any? {
     switch self {
     case let .simple(filter):
       if !arguments.isEmpty {
         throw TemplateSyntaxError("cannot invoke filter with an argument")
       }
-
       return try filter(value)
     case let .arguments(filter):
-      return try filter(value, arguments)
+      return try filter(value, arguments, context)
     }
   }
 }