lang: replace stack-based parser with a recursive parser

lang/parse/index.c

@@ -0,0 +1,37 @@
+#include "ctx.h"
+
+#include <ivy/lang/ast.h>
+
+bool parse_index(
+	struct ivy_parser *parser, struct ivy_ast_node *container,
+	struct ivy_ast_node **out)
+{
+	if (!parse_symbol(parser, IVY_SYM_LEFT_BRACKET)) {
+		parse_trace(parser, "expected `[` before subscript value");
+		return false;
+	}
+
+	struct ivy_ast_node *subscript = NULL;
+	if (!parse_expr(parser, EXPR_PARSE_NORMAL, &subscript)) {
+		parse_trace(parser, "invalid subscript value");
+		return false;
+	}
+
+	if (!parse_symbol(parser, IVY_SYM_RIGHT_BRACKET)) {
+		parse_trace(parser, "expected `]` after subscript value");
+		return false;
+	}
+
+	struct ivy_ast_op_node *op_node = create_node(IVY_AST_OP);
+	if (!op_node) {
+		return false;
+	}
+
+	op_node->n_op = ivy_operator_get_by_id(IVY_OP_SUBSCRIPT);
+	op_node->n_left = container;
+	op_node->n_right = subscript;
+
+	*out = generic_node(op_node);
+
+	return true;
+}