Re: Better way to code an iterator function?

["Lawrence E. Bakst" <ml@...>]

Backtracking the index was one of the things that was bugging me. I think I like your code better, although it's the same number of lines and adds a local variable.

Thanks.

leb

>function it_paths(paths)
>   local function next(state, var)
>       local result
>       result, state.idx = paths[state.idx], state.idx+1
>       return result
>   end
>   local state = {idx = 1 };
>   return next, state, "";
>end;


At 6:08 PM +1100 10/23/09, Mark Feldman wrote:
>Are you trying to avoid backtracking the index or keeping its previous value? How about this:
>
>function it_paths(paths)
>   local function next(state, var)
>       local result
>       result, state.idx = paths[state.idx], state.idx+1
>       return result
>   end
>   local state = {idx = 1 };
>   return next, state, "";
>end;
>
>Mark Feldman
>
>Lawrence E. Bakst wrote:
>>1. Is there a better, shorter, cuter, or cooler way to code the example below?
>>
>>2. I guess something I didn't try was to "deep copy" paths, use that as the state, and then remove one element at a time from the state.
>>
>>3. This is probably FAQ, but I couldn't find much with a quick search on Google.
>>
>>I miss C's pre/post inc/dec operators and I can't be the only one. Is there any way to make inc and dec functions that increment or decrement the number passed in and return the previous value? Seems difficult in a language that only has pass by value for numbers and strings.
>>
>>Thanks in advance for all help and suggestions.
>>
>>function it_paths(paths)
>>    local function next(state, var)
>>        if (state.idx > #paths) then return nil end;
>>        state.idx = state.idx + 1;
>>        return paths[state.idx - 1];
>>    end
>>    local state = {idx = 1};
>>    return next, state, "";
>>end;
>>
>>function process_random_files(paths)
>>    for path in it_paths(paths) do
>>        print(path);
>>    end
>>end
>>
>>process_random_files{"foo", "bar", "baz", "quuz"};
>>
>> 
>
>
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-- 
leb@iridescent.org