On Thu, 2005-08-18 at 10:20 +0200, Andrej Bauer wrote:
> Contrary to what skaller says, no inductive types are allowed in a
> polynomial functor. 

This isn't contrary to what I said: I didn't say inductive types
were allowed, I said the polynomial could be built *using*
induction. 

EG: 1 is a list, if L is a list then T * L is a list. It follows
T is a list, T * T is a list .. etc, and so a list is given
by the polynomial

	1 + T + T * T + T * T * T + ...

I accept this may not be the most general definition.
You said later:

"Such types are well
understood and have accompanying induction and recursion principles from
which various operations (map, fold, etc.) can be built systematically."

and I wonder why no production languages actually do that...

-- 
John Skaller <skaller at users dot sourceforge dot net>