Function error

demos/lib/Mental.js:6933–6943

(str)

                var parseTreeOutput = '', converted, pos = 0, chr, index, result;

                function error(str) {
                    var e = new Error();
                    throw {
                        msg : str + (e.stack ? ' - ' + e.stack : ''),
                        pos : pos,
                        chr : typeof chr === 'undefined' ? '(end)' : chr,
                        state : parseTreeOutput,
                        text : code.slice(pos - 10, pos + 10),
                        code : this.code
                    };
                }

                function execute(code) {
                    var result;