expect method
Check current token and some tokens after it to see if the types match,
return a boolean result.
If consume is true, will advance.
Implementation
bool expect(List<String> lexemes, {bool consume = false}) {
for (var i = 0; i < lexemes.length; ++i) {
if (peek(i).lexeme != lexemes[i]) {
return false;
}
}
if (consume) {
advance(lexemes.length);
}
return true;
}