[Caml-list] Recursive polymorphic variants

[Caml-list] Recursive polymorphic variants

[Gabriel Kerneis]

Hi list,

why is this definition allowed:
    type t = [`A of t]
but the following one fails:
    type t = [`A of [t|`B]]
    Error: The type constructor t is not yet completely defined

Is there any work-around?

(My actual example is much larger and complex but I think it boils down to this
simple case.)

Many thanks,
-- 
Gabriel Kerneis

Re: [Caml-list] Recursive polymorphic variants

[David House]

On Tue, Apr 10, 2012 at 2:51 PM, Gabriel Kerneis <kerneis@pps.jussieu.fr> wrote:
> Is there any work-around?

Depending on your requirements, just wrapping up the recursive copy of
[t] in another constructor might do:

type t = [ `A of [ `B | `C of t ]]

I don't know why your original example is disallowed.

Re: [Caml-list] Recursive polymorphic variants

[Romain Bardou]

Le 10/04/2012 15:57, David House a écrit :
> On Tue, Apr 10, 2012 at 2:51 PM, Gabriel Kerneis<kerneis@pps.jussieu.fr>  wrote:
>> Is there any work-around?
>
> Depending on your requirements, just wrapping up the recursive copy of
> [t] in another constructor might do:
>
> type t = [ `A of [ `B | `C of t ]]
>
> I don't know why your original example is disallowed.
>

I think the semantic of [t|...] is just to syntactically replace t by 
its definition, which is not possible if the definition is not done yet.

Cheers,

-- 
Romain Bardou