public sealed override InternalResult <Unit> Parse(ref ParseState <TToken> state) { if (state.HasCurrent) { state.Error = new InternalError <TToken>( Maybe.Just(state.Current), false, state.Location, null ); state.AddExpected(new Expected <TToken>()); return(InternalResult.Failure <Unit>(false)); } return(InternalResult.Success(Unit.Value, false)); }