Re: [Caml-list] Questions about default instances

["Sébastien Furic" <programming.languages@furic.org>]

  Hello Jacques,

Le 08/08/2011 09:14, Jacques Garrigue a écrit :
> On 2011/08/05, at 1:22, Sébastien Furic wrote:
>
>> What is the usual way in OCaml to define mutually recursive classes that share default instances?
>
> There is no concept of "default instance" in OCaml, and as you discovered yourself,
> default instances create problems with initialization.
> Namely, an object constructor might attempt to access a default instance before it is built,
> so we need a way to know whether it is ready or not.

  But I still wonder why it is not possible to allow “direct let rec” in 
my example. Indeed, object creation is safe here since access to default 
instances is protected by method calls (there is a potential problem 
with initializers that may refer to, or call methods that refer to, 
not-yet-initialized objects but this can be statically checked, can't 
it?). As a benefit, it would avoid using lazy values in singleton 
patterns (which make the whole thing a bit unreadable IMO) and, in 
particular, the definition of not_ in my example would be more natural 
(I think about the poor readers of my code but also raw performance).

  Cheers,

  Sébastien.