Naive implementation of Either in JAva

gistfile1.java

package bad.robot;

import fj.F;

import java.util.function.Function;
import java.util.stream.Stream;

public interface Either<A, B> {

	static <A, B> Either<A, B> left(final A a) {
		return new Left<>(a);

	}

	static <A, B> Either<A, B> right(final B b) {
		return new Right<>(b);
	}

	static <T, R> Function<T, Either<Pair<T, Throwable>, R>> asEithers(Function<T, R> function) {
		return (T a) -> {
			try {
				return Either.<Pair<T, Throwable>, R>right(function.apply(a));
			} catch (Throwable e) {
				return left(Pair.pair(a, e));
			}
		};
	}

	Boolean isLeft();
	Boolean isRight();
	Stream<A> left();
	Stream<B> right();

	class Left<A, B> implements Either<A, B> {

		private final A value;

		public Left(A value) {
			this.value = value;
		}

		@Override
		public Boolean isLeft() {
			return true;
		}

		@Override
		public Boolean isRight() {
			return false;
		}

		@Override
		public Stream<A> left() {
			return Stream.of(value);
		}

		@Override
		public Stream<B> right() {
			return Stream.empty();
		}
	}

	class Right<A, B> implements Either<A, B> {
		private final B value;

		public Right(B value) {
			this.value = value;
		}

		@Override
		public Boolean isLeft() {
			return false;
		}

		@Override
		public Boolean isRight() {
			return true;
		}

		@Override
		public Stream<B> right() {
			return Stream.of(value);
		}

		@Override
		public Stream<A> left() {
			return Stream.empty();
		}
	}
}