Re: [Caml-list] About Obj (was Recursive lists)

[Christophe Raffalli <christophe.raffalli@univ-savoie.fr>]

james woodyatt wrote:
> On 11 Oct 2004, at 06:38, Christophe Raffalli wrote:
> 
>> Jean-Christophe Filliatre wrote [quite sensibly]:
>>
>>>
>>> [...]
>>> This shouldn't be advised, and not even posted on this list.
>>
>>
>> And how do you write a tail recursive map doing only one structure 
>> traversal (which is important with the penalty for memory access) on 
>> immutable list without the Obj module ?
> 
> 
> By using a more appropriate data structure, e.g. a lazy list.  It's a 
> pay-me-now-or-pay-me-later sort of game you're playing here.
> 
> Rather than whack on the immutable list, maybe you should consider doing 
> this:
> 
>     type 'a mlist = N | C of 'a mcell
>     and 'a mcell = { mutable cdr: 'a; mutable car: 'a mlist }

This data structure uses 5 words and 2 indirection per cons cell 
(instead of 3 and 1 for standard list). So it will be slower on all 
operations. Moreover you may want immutable list with tail recursive and 
  one mono-traversal map and fold_right.




-- 
Christophe Raffalli
Université de Savoie
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