public override T Eval()
{
TailCall <T> tailRec = this;
while (tailRec.IsSuspend())
{
tailRec = tailRec.Resume();
}
return(tailRec.Eval());
}
private static TailCall <BigInteger> Sum(BigInteger arg, BigInteger acc)
{
return(arg == 0
? (TailCall <BigInteger>) TailCall <BigInteger> .Ret(acc)
: TailCall <BigInteger> .Sus(() => Sum(arg - 1, acc + arg)));
}