Re: Memoizing Functions - yet another attempt

[Sir Pogsalot <sir.pogsalot@...>]

On Sun, Dec 15, 2013 at 8:05 AM, Sir Pogsalot <sir.pogsalot@gmail.com> wrote:

On Sun, Dec 15, 2013 at 7:55 AM, Sir Pogsalot <sir.pogsalot@gmail.com> wrote:

On Sat, Dec 14, 2013 at 10:53 PM, Tim Hill <drtimhill@gmail.com> wrote:

On Dec 14, 2013, at 2:01 PM, Petite Abeille <petite.abeille@gmail.com> wrote:

>
> On Dec 14, 2013, at 10:19 PM, Tim Hill <drtimhill@gmail.com> wrote:
>
>> Translation: Only pure functions should be candidates for memoization.
>
> Eh? Since when? I, for one, see great, concrete, tangible benefit in memoizing, say, that very expensive network call  for whatever period of time I personally see fit.
>
>

In which case you are essentially asserting to yourself that, under acceptable constraints, that expensive network call IS (in effect) a pure function.

—Tim

Teeeechnically it would be impure every time because networking means I/O. :>

Though I'd still be okay with that if it's fetching a static page and the call succeeded (verified from what got returned)... or you know the period between updates to the page so you can memoized.forget() it and rerun. :>

Anyway, this got me to thinking that it would be useful to remove the cached return values for a specific call -- if the function is impure and you know the cache needs updating.

So then, `clear' in the module I posted becomes:

local clear =

    function (f, ...)

        -- reset everything if called without args

        if not f then

            -- replace/clear guid table, guid counter, drop function call caches

            guids   = setmetatable({}, { __mode = 'k' })

            counter = 0

            funcs   = {}

            return  

        end 

        

        -- only the function was provided, forget the

        -- cached returns for every call made to `f'

        if select('#', ...) == 0 then

            funcs[f] = nil

            return

        end 

        

        -- an arglist was provided, remove

        -- this specific call signature cache

        if funcs[f] then

            funcs[f][args_to_str(...)] = nil

        end 

    end 

It *might* be useful to forget a specific call while keeping the memoized returns of all others.

It allows you to just write: memoize.forget(table.pack, 1, 2, 3)

The next memoize(table.pack, 1, 2, 3) will re-cache the returned value.

(Let's pretend this was a better example with an impure function)

Toodles :-)

I immediately notice a problem with that ammendation I made to the `clear' function.  You can't clear a specific no-arg call, and the only way to remove that is to forget all memoized calls at once.  So blah.

I'd probably separate this into: memoize.forget_everything(), memoize.forget_function(), and memoize.forget_call()

Blah!