Either.kt

sealed class Either<out L, out R> {
    class Left<out T>(val value: T) : Either<T, Nothing>() {
        override fun equals(other: Any?): Boolean =
                other is Left<*> && other.value == value

        override fun hashCode(): Int = value?.hashCode() ?: 0

        override fun toString(): String = "Left($value)"
    }

    class Right<out T>(val value: T) : Either<Nothing, T>() {
        override fun equals(other: Any?): Boolean =
                other is Right<*> && other.value == value

        override fun hashCode(): Int = value?.hashCode() ?: 0

        override fun toString(): String = "Right($value)"
    }
}