:art: Add default arguments

diff --git a/ast b/ast
index 9d0aeac53100a9d62a368cd7ed418c5f21487e16..47451b4dde1405956a8635d5f4850beb5ced6402 160000 (submodule)
--- a/ast
+++ b/ast
@@ -1 +1 @@
-Subproject commit 9d0aeac53100a9d62a368cd7ed418c5f21487e16
+Subproject commit 47451b4dde1405956a8635d5f4850beb5ced6402