t.mapLeft { it + 1 }.right == "a"
    t.mapRight { it * 2 }.left == 1
    t.mapRight { it * 2 }.right == "aa"

    t.nestLeft(2).mapLeft(unpackLeft()).left == 2
    t.nestLeft(2).mapLeft(unpackRight()).left == 1
    t.nestLeft(2).mapLeft(unpackLeft()).right == "a"
    t.nestLeft(2).mapLeft(unpackRight()).right == "a"
    t.nestRight(2).mapRight(unpackLeft()).right == 2
    t.nestRight(2).mapRight(unpackRight()).right == "a"

    /**
     * Map the left side.
     *
     * @see #mapRight
     * @see #fold
     */
    public abstract <U, V> Either<U, V> mapLeft(Function<? super L, ? extends U> f);

    /**
     * Map the right side.
     *
     * @see #mapLeft
     * @see #fold
     */
    public abstract <U, V> Either<U, V> mapRight(Function<? super R, ? extends V> f);

    /**

        right.right.get() == RIGHT
    }

    def "map() works"() {
        expect:
        left.mapLeft({ assert it == LEFT; LEFT2 }).left.get() == LEFT2
        left.mapRight({ assert false }).left.get() == LEFT

        right.mapRight({ assert it == RIGHT; RIGHT2 }).right.get() == RIGHT2
        right.mapLeft({ assert false }).right.get() == RIGHT
    }

    def "fold() subsumes flatMap()"() {
        expect:

    }

    public <T> Pair<T, R> mapLeft(Function<? super L, ? extends T> function) throws Exception {
        return of(function.apply(left), right);
    }

    public <T> Pair<L, T> mapRight(Function<? super R, ? extends T> function) throws Exception {
        return of(left, function.apply(right));
    }

    @Nullable
    public <T> T map(Function<? super Pair<L, R>, ? extends T> function) throws Exception {

	}

	return true, nil
}

func capright(idx uint64, bit uint64) uint64 {
	return ((1 << (57 + idx)) | bit)
}

// CapRightsInit returns a pointer to an initialised CapRights structure filled with rights.
// See man cap_rights_init(3) and rights(4).
func CapRightsInit(rights []uint64) (*CapRights, error) {
	var r CapRights
	r.Rights[0] = (capRightsGoVersion << 62) | capright(0, 0)
	r.Rights[1] = capright(1, 0)