lang: ast: re-write expression parser to support keyword messages

also adjust some parser state callbackss to better support sub-parsers returning
 results to their parents.

lang/ast/unit-package.c

@@ -57,12 +57,6 @@ static struct token_parse_result parse_linefeed(
 	return PARSE_RESULT(IVY_OK, 0);
 }
 
-static enum ivy_status add_child(
-	struct ivy_ast_node *parent, struct ivy_ast_node *child)
-{
-	return IVY_ERR_NOT_SUPPORTED;
-}
-
 static void print(struct ivy_ast_node *node)
 {
 	struct ivy_ast_unit_package_node *unit_package
@@ -94,7 +88,6 @@ static void init_state(struct ivy_parser *ctx, struct parser_state *sp)
 }
 
 struct ast_node_type unit_package_node_ops = {
-	.n_add_child = add_child,
 	.n_print = print,
 	.n_init_state = init_state,
 	.n_state_size = sizeof(struct unit_package_parser_state),
@@ -107,4 +100,4 @@ struct ast_node_type unit_package_node_ops = {
 		TOK_PARSER(LINEFEED, parse_linefeed),
 	}
 
-};
+};