Re: a question about memoization

Stephen J. Bevan wrote:
> Jon Harrop <usenet@[EMAIL PROTECTED]
> writes:
>> In F#:
>>
>>   let memoize f =
>>     let m = Hashtbl.create 1
>>     fun x ->
>>       try m.[x] with Not_found ->
>>       let f_x = f x
>>       m.[x] <- f_x
>>       f_x
>>
>> The critical point is that the hash and equality functions are carried
in
>> the type automatically and do not need to be supplied separately by
hand.
>> This solution combined the correctness of SML with brevity of OCaml.
> 
> I'm quoting the above because it is the shortest, not because it is
> the only code with this issue: how do I flush the cache or is this an
> academic problem rather than a practical one?

The solution is still a practical one because there are many cases where
unbounded memoization is acceptable. For example, when loading glyphs.

Rather than providing an explicit "flush" function you would typically
replace the Hashtbl with something more appropriate, such as a weak hash
table that allows bindings to be garbage collected once it exceeds a
certain size, a round-robin scheme or a more sophisticated collection
strategy.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/products/?u