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package net.eusashead.parquet.util;

public abstract class Option implements Monad {

	public static  Option some(F f) {
		if (f != null) {
			return new Some<>(f);
		} else {
			return none();
		}
	}

	public static  Option none() {
		return new None<>();
	}

	public abstract boolean has();

	public abstract F get();
	
	public abstract  T maybe(T def, Function function);
	
	@Override
	public abstract  Option bind(Function function);

}

class None extends Option {

	@Override
	public boolean has() {
		return false;
	}

	@Override
	public F get() {
		throw new IllegalStateException();
	}

	@Override
	public  Option bind(
			Function function) {
		return new None();
	}
	
	@Override
	public  T maybe(T def,
			Function function) {
		return def;
	}

}

class Some extends Option {

	private final F b;

	Some(F b) {
		this.b = b;
	}

	@Override
	public boolean has() {
		return true;
	}

	@Override
	public F get() {
		return b;
	}

	@Override
	public  Option bind(
			Function function) {
		return Option.some(function.apply(b));
	}
	
	@Override
	public  T maybe(T def,
			Function function) {
		return function.apply(b);
	}
}