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/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
	import java.util.function.Function;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
 
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 final T val;
}
 
 
	public static void main (String[] args) throws java.lang.Exception
	{
		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() );
	}
}

Main.java:38: error: non-static variable this cannot be referenced from a static context
		Maybe<Integer> x = new Maybe<>(5);
		                   ^
Main.java:39: error: non-static variable this cannot be referenced from a static context
		Monad<Integer> y = x.bind(v -> new Maybe<Integer>(v+1))
		                               ^
Main.java:40: error: non-static variable this cannot be referenced from a static context
		                    .bind(v -> new Maybe<Integer>(v*2));
		                               ^
3 errors

Standard output is empty