function fooIter(n,x)
 local i = string.len(x)

 if i < 10 then
   if 0 == i%2 then
     return x,true
   else
     return x,false
   end
 end

 return nil
end

function foo(s)
 return fooIter,nil,s
end

local N = 0
for p,s in foo("d") do
 N = N + 1
 print(N, p, s)
 if( s ) then
   p = p .. "o"
 else
   p = p .. "x"
 end
 if N > 15 then break end
end

1	d	false
2	d	false
3	d	false
4	d	false
5	d	false
6	d	false
7	d	false
8	d	false
9	d	false
10	d	false
11	d	false
12	d	false
13	d	false
14	d	false
15	d	false
16	d	false