Recursion

["Dirien B. Perez" <dperez@newtimes.com>]

Hi I am having some problems with recursion I have the iterative 
version of a function that will calculate the sum of the elements is a
linked list:

	function sum(list:cell_ptr) return integer is
	local:cell_ptr:=list;
	s:integer:=0;
	begin
		while local /= null loop	
		s:=s+local.value;
		local:=local.next
		end loop;
	return s;
	end sum;
I need help creating the recursion version. Also I need to createa
recursive definition of the set of all positive numbers containing only
the digits 3,5 and 9.

I appreciate any help that I can get...... and thank you in advance.
future ada programmer..