Re: Is it possible to make a possibly self-referential type using containers?

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2016-07-31 02:31, Shark8 wrote:

> Type Executable_Code(<>) is private; -- The type in which we store executable code.
> Type Word(<>);
>
> Package Word_List is new Ada.Containers.Indefinite_Vectors
>   (Element_Type => Word, Index_Type => Positive);
>
> Type Word( Is_List ) is record
>   case Is_List is
>     when True  => List : Word_List.Vector;
>     when False => Item : Executable_Code;
> end record;
>
> The above would be nicely elegant insofar as maintenance goes as
> it's  simple and straightforward.

Nothing elegant in this, but anyway...

> * Word: a chunk of code to execute or a list of words [to execute].
> ** Something like SEQUENCE OF INTEGER is fundamental in IDL and ASN.1.

    type Word is interface;
    type Executable_Code (<>) is new Word with private;
    package Lists is
       new Ada.Containers.Indefinite_Vectors
           (  Index_Type   => Positive,
              Element_Type => Word'Class
           );
    type List is new Lists.Vector and Word with null record;

P.S. Type recursion is inconsistent if not resolved, as in the example 
which splits self-referential Word into Word interface and Word'Class.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de