Iteration for Factorials

[Tim Chase]

> Still, why do you want None instead of raisng an exception
> (as is the case in other factorial implementations)?

A null value is as good/bad as raising an exception in my book.
Since you can't do math on a None object, any attempt to do so
will raise an exception:

  >>> 42 + fact(-1)

I generally prefer my functions to return semi-sensible results
(in this case, None makes sense to me, as there isn't really a
definition of "negative-one factorial").  It also fits in my head
alongside my SQL where NULL values/expressions can be returned
and evaluated without the whole query falling over.

I suppose if you really wanted to throw an exception using this
lambda craziness, you could wrap the whole result in "0 +
([body])" which, if the body returned Null, would push up
exception daisies (with slightly misleading exception information).

-tkc