import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;

public final class MonadList {

	public static void main(String[] aArgs) {
		Monad<Integer> integers = Monad.unit(List.of( 2, 3, 4 ));
	    Monad<String> strings = integers.bind(MonadList::doubler).bind(MonadList::letters);
	    System.out.println(strings.getValue());
	}
	
	private static Monad<Integer> doubler(List<Integer> aList) {
		return Monad.unit(aList.stream().map( i -> 2 * i ).toList());
	}
	
	private static Monad<String> letters(List<Integer> aList) {
		return Monad.unit(aList.stream().map( i -> Character.toString((char) (64 + i)).repeat(i) ).toList());		
	}
	
}

final class Monad<T> {		
	
	public static <T> Monad<T> unit(List<T> aList) {
		return new Monad<T>(aList);
	}
	
	public <U> Monad<U> bind(Function<List<T>, Monad<U>> aFunction) {
		return aFunction.apply(list);
	}
	
	public List<T> getValue() {
		return list;
	}
	
	private Monad(List<T> aList) {
		list = new ArrayList<T>(aList);
	}
	
	private List<T> list;
	
}