Memoizing Functions - yet another attempt

[Andrew Starks <andrew.starks@...>]

On Saturday, December 14, 2013, Petite Abeille  wrote:
> On Dec 14, 2013, at 7:53 PM, Dirk Laurie <dirk.laurie@gmail.com> wrote:
>
> > Is this a question?
>
> Nah. More of a puzzlement really.
>
> Let take a closer look at that Microlight's memoize function [1]:
>
> (1) It mandates one parameter (not zero, not multiple parameters, just one, not nil, parameter) [2]
> (2) It mandates one return value (not zero, not multiple return values, just one, not nil return value) [3]
> (3) It prevent parameters from ever being garbage collected
>
> I totally fail to say how such ‘most inflexible solution of all … is the only useful way to do it’.
>
>
> [1] https://github.com/stevedonovan/Microlight/blob/master/ml.lua#L799
> [3] Curiously, the implementation sports varargs, even though they cannot be used in  practice
>
> local k = 0
> f = memoize(function( ... ) k = k + 1 return k end)
>
> f()
> table index is nil
> stack traceback:
>         TestMem.lua:5: in function '__index'
>         TestMem.lua:8: in function 'f'
>         TestMem.lua:16: in main chunk
>
> f( 1 )
> f( 1, 2 )
> f( 1, 2, 3 )
> print( k )
>
> > 1
>
> [3] In fact, if a function happen to return nil it will be evaluated over and over, defeating the entire purpose of the exercise.
>
> local k = 0
> f = memoize(function( ... ) k = k + 1 return nil end)
>
> f( 1 )
> f( 2 )
> f( 3 )
> print( k )
>
> > 3

The argument list is:

function(k, ...)

So, it only memoizes on the first argument but accepts many. There must be a general use case for this, but it isn't clear to me what that would be.

Anyone care to edumicate?