Re: [Caml-list] Recursive lists

["Sébastien Furic" <sebastien.furic@tni-software.com>]

Luca Pascali wrote:

> Hi everyone.
> 
> I have a little question about the recursive lists.
> In an application I needed to use a list composed by some elements 
> (placed in the head of the list) and recursive element, like
> 
> let rec_list =
>    let rec l2 = 100 :: l2 in
>       [1;2;3;4;5] @ l2
> 
> in order to have the last elements periodically repeated.
> In a list like this, I found that the map function goes in stack 
> overflow. It seems that it is not aware of the recursive characteristics 
> of the input list.
> I had to write a version of the map function to support this in my 
> software (I have to finalize something before posting it).
> 
> My questions are:
> Can some functions of the List library support the use of the recursive 
> lists?
> I mean: can some scanning functions such as map, for_all, exists, mem, 
> filter, and so on understand if they are working on recursive lists and 
> act correctly without going in buffer overflow or infinite loops?
> Did anyone already have a similar needing? And in which way did he/she 
> work?
> 
> Thanks in advance to anyone
> 
> Luca
> 
> 

  You can use lazy lists to solve the problem. A lazy list delivers its 
elements on demand so you can manipulate infinite lists safely provided 
you don't print their whole contents for instance...
  See http://caml.inria.fr/archives/200304/msg00280.html to see how to 
implement them (they're not present in the OCaml distribution).

  Sébastien.

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