public static DataType Fupdate(Del f, int i, DataType ts)
{
if (ts is One one)
{
if (i == 0)
{
return(new One(f(one.Alpha), one.RList));
}
return(Cons(one.Alpha, Fupdate(f, i - 1, new Zero(one.RList))));
}
if (ts is Zero zero)
{
RList <Tuple <T, T> > .Del fp0 = value => new Tuple <T, T>(f(value.Item1), value.Item2);
RList <Tuple <T, T> > .Del fp1 = value => new Tuple <T, T>(value.Item1, f(value.Item2));
var fp = i % 2 == 0 ? fp0 : fp1;
return(new Zero(RList <Tuple <T, T> > .Fupdate(fp, i / 2, zero.RList)));
}
throw new ArgumentException("must be Zero or One", nameof(ts));
}
