fail method
Implementation
dynamic fail({Token? tok, String? expected, String? message}) {
if (tok == null) tok = token!;
if (message == null) {
if (expected != null) {
message = "Expected $expected but found $tok";
}else{
message = "Unexpected token $tok";}
}
// throw new ParseError(
// message, filename, tok.line, tok.startOffset, tok.endOffset);
}