lang: replace stack-based parser with a recursive parser

lang/parse/package-import.c

@@ -0,0 +1,49 @@
+#include "ctx.h"
+
+#include <ivy/lang/ast.h>
+
+bool parse_package_import(struct ivy_parser *parser, struct ivy_ast_node **out)
+{
+	if (!parse_keyword(parser, IVY_KW_USE)) {
+		parse_trace(
+			NULL, "expected `use` before package import statement");
+		return false;
+	}
+
+	struct ivy_ast_unit_import_node *unit_import
+		= create_node(IVY_AST_UNIT_IMPORT);
+
+	struct ivy_token *tok = NULL;
+	if (!parse_word(parser, &tok)) {
+		parse_trace(NULL, "expected word after `use` keyword");
+		return false;
+	}
+
+	fx_queue_push_back(&unit_import->n_ident, &tok->t_entry);
+
+	while (1) {
+		if (parse_linefeed(parser)) {
+			break;
+		}
+
+		if (!parse_symbol(parser, IVY_SYM_DOT)) {
+			parse_trace(
+				NULL,
+				"expected linefeed or `.` after package "
+				"identifier word");
+			destroy_node(unit_import);
+			return false;
+		}
+
+		if (!parse_word(parser, &tok)) {
+			parse_trace(NULL, "expected word after `use` keyword");
+			destroy_node(unit_import);
+			return false;
+		}
+
+		fx_queue_push_back(&unit_import->n_ident, &tok->t_entry);
+	}
+
+	*out = generic_node(unit_import);
+	return true;
+}