import java.util.function.Function;

interface Monad<T> {
    public <U> Monad<U> bind(Function<T, Monad<U>> f);
}

class Maybe<T> implements Monad<T> {
    public Maybe(T val) {
        this.val = val;
    }

    public T getVal() {
        return val;
    }

    @Override
    public <U> Monad<U> bind(Function<T, Monad<U>> f) {
        if (val == null)
            return new Maybe<U>(null);
        return f.apply(val);
    }

    private T val;
}

public class MonadApp {
    public static void main(String[] args) {
        Maybe<Integer> x = new Maybe<>(5);
        Monad<Integer> y = x.bind(v -> new Maybe<Integer>(v+1))
                            .bind(v -> new Maybe<Integer>(v*2));
        System.out.println( ((Maybe<Integer>)y).getVal() );
    }
}