Add PlainListItem to ast nodes.

src/iter/macros.rs

@@ -1,3 +1,16 @@
+/// Write the implementation of From<> to convert a borrow of the type to an AstNode
+macro_rules! to_ast_node {
+    ($inp:ty, $enum:expr) => {
+        impl<'r, 's> From<$inp> for AstNode<'r, 's> {
+            fn from(value: $inp) -> Self {
+                $enum(value)
+            }
+        }
+    };
+}
+
+pub(crate) use to_ast_node;
+
 /// Create iterators for ast nodes where it only has to iterate over children
 macro_rules! children_iter {
     ($astnodetype:ty, $itertype:ident, $innertype:ty) => {