Re: lua idiom: iteration with skips?

["Matthew M. Burke" <mmburke@...>]

Gregg Reynolds wrote:

> I need to iterate over a list of items with skip logic.  For example, if
> item[i] fits some criteria, then skip to item[i+n] else skip to item[i+m].
>
> If I understand the manual, altering an iteration variable is a no-no,
> so I can't use a for loop for this.


Here's yet another way to skin this cat.  I think it's fairly lua-ish
because a number of other languages don't allow you to take this approach:



function hopscotch(table, processor)
  local index = 1
  return function ()
           if (table[index] == nil) then
              return nil
           else
              local i = index
              index = index + processor(table[index])
              return i, table[i]
           end
        end
end


t = {20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
37, 38, 39}

--- if the value is even, we'll skip ahead 3
-- otherwise, we'll skip ahead 5
function p(v)
   if ( math.floor(v/2) == v/2) then
      return 3
   else
      return 5
   end
end


for k,v in hopscotch(t, p) do
   print(k, v)
end



Matt