-"nil" L C I(identifier, Identifier("nil"), tk::Identifier_, hi::Constant);
+
+"NULL" L C I(identifier, Identifier("NULL"), tk::Identifier_, hi::Constant);
+"nil" L C I(identifier, Identifier("nil"), tk::Identifier_, hi::Constant);
+"YES" L C I(identifier, Identifier("YES"), tk::Identifier_, hi::Constant);
+"NO" L C I(identifier, Identifier("NO"), tk::Identifier_, hi::Constant);