Re: Map and filter without intermediate tables

[Geoff Leyland <geoff_leyland@...>]

On 7/06/2012, at 6:52 PM, Dirk Laurie wrote:

> 2012/6/7 Geoff Leyland <geoff_leyland@fastmail.fm>:
> 
>> Is it a dead-end idea, or is it that my implementation [1] is brain dead?
> 
> I read the code up to line 34.  Five function-valued local variables,
> three of them coded in Lua (not C), had by then been expended to simulate
> (presumably for the sake of compatibility with Lua 5.1) something that
> comes free of charge in Lua 5.2.
> 
> So my first suggestion is:
> 
> ---
> 
> local pairs, ipairs = pairs, ipairs
> if _VERSION~="Lua 5.2" then
>  -- put those lines here, changing `local function pairs` to
>  -- `pairs = function` etc
> end
> 
> ---
> 
> and at least under Lua 5.2 you should see some improvement.

5.2 does make a small difference, and it's somewhat positive, but it doesn't make intermediate-free implementations better than ones with intermediate tables.

In the "real" code, pairs takes extra arguments: extended_pairs(table_like_thing, some, context), which it then passes on to the iterator, so I can't use 5.2's pairs anyway.