Add ls

Change-Id: I86f799ff9577940c7df8e01cda6c6b7867de8e7e
diff --git a/src/ast_handlers.hpp b/src/ast_handlers.hpp
index b58613c..2953dad 100644
--- a/src/ast_handlers.hpp
+++ b/src/ast_handlers.hpp
@@ -204,6 +204,8 @@
 };
 
 
+struct ls_class;
+
 struct cd_class {
     template <typename Iterator, typename Exception, typename Context>
     x3::error_handler_result on_error(Iterator&, Iterator const&, Exception const& x, Context const& context)