lang: replace stack-based parser with a recursive parser

lang/parse/unit.c

@@ -0,0 +1,50 @@
+#include "ctx.h"
+
+#include <ivy/lang/ast.h>
+
+bool parse_unit(struct ivy_parser *parser, struct ivy_ast_node **out)
+{
+	struct ivy_ast_unit_node *unit
+		= (struct ivy_ast_unit_node *)ivy_ast_node_create(IVY_AST_UNIT);
+	if (!unit) {
+		parser->p_status = IVY_ERR_NO_MEMORY;
+		return false;
+	}
+
+	bool result = true;
+	bool prev_was_expr = false;
+	while (1) {
+		struct ivy_ast_node *child = NULL;
+
+		if (parse_eof(parser)) {
+			break;
+		}
+
+		if (parse_linefeed(parser)) {
+			continue;
+		}
+
+		if (peek_keyword(parser, IVY_KW_PACKAGE)) {
+			result = parse_package_id(parser, &child);
+		} else if (peek_keyword(parser, IVY_KW_USE)) {
+			result = parse_package_import(parser, &child);
+		} else if (peek_keyword(parser, IVY_KW_CLASS)) {
+			result = parse_class(parser, &child);
+		} else if (peek_expr_start(parser)) {
+			result = parse_expr(
+				parser, EXPR_PARSE_CONSUME_TERMINATOR, &child);
+		} else {
+			parse_trace(parser, "unexpected token");
+			result = false;
+		}
+
+		if (!result || !child) {
+			break;
+		}
+
+		fx_queue_push_back(&unit->n_children, &child->n_entry);
+	}
+
+	*out = generic_node(unit);
+	return result;
+}