code: function(top) {
      const result = this.node("block");
      this.expect("{") && this.next();
      const body = top
        ? this.read_top_statements()
        : this.read_inner_statements();
      this.expect("}") && this.next();
      return result(null, body);
    }
docs: ```ebnf
  code_block ::= '{' (inner_statements | top_statements) '}'
  ```