paolilleither.cs

paolilleither.cs

internal interface Either<L, R>
{
    Either<L, B> Bind<B>(Func<R, Either<L, B>> f);

    B Match<B>(Func<L, B> whenLeft, Func<R, B> whenRight);
}

internal sealed record Right<L, R> : Either<L, R>
{
    private readonly R _right;

    internal static Either<L, R> Return(R r) => new Right<L, R>(r);

    private Right(R right)
    {
        _right = right;
    }

    Either<L, B> Either<L, R>.Bind<B>(Func<R, Either<L, B>> f) => f(_right);

    B Either<L, R>.Match<B>(Func<L, B> _, Func<R, B> whenRight) => whenRight(_right);
}

internal sealed record Left<L, R> : Either<L, R>
{
    private readonly L _left;

    internal Left(L left)
    {
        _left = left;
    }

    Either<L, B> Either<L, R>.Bind<B>(Func<R, Either<L, B>> _) =>
        new Left<L, B>(_left);

    B Either<L, R>.Match<B>(Func<L, B> whenLeft, Func<R, B> whenRight) => 
        whenLeft(_left);
}