public static Io <A> Also <A, B>(Io <A> a, Io <B> b) => a.Also(b);
public static Io <B> Then <A, B>(Io <A> a, Io <B> b) => a.Then(b);
public static Func <A, Io <B> > Demote <A, B>(Io <Func <A, B> > f) => x => Of(() => f.Eval().Invoke(x));
private static A Eval <A>(Io <A> io) => io.Eval();
public static Io <A> Flatten <A>(this Io <Io <A> > io) => Of(() => io.Eval().Eval());
