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From: Natasha Kerensikova <lithiumcat@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: S-expression I/O in Ada
Date: Sun, 22 Aug 2010 10:43:02 +0000 (UTC)
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On 2010-08-19, Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org> wrote:
>> And if there is no other way, would it make sense to get rid of the
>> discriminant with something like:
>>
>> type S_Expression is tagged null record;
>>
>> package Lists is new Ada.Containers.Indefinite_Doubly_Linked_List
>>                       (Element_Type =>  S_Expression'Class);
>>
>> type Atom_Node is new S_Expression with record
>>     Value : Atom;
>> end record;
>>
>> type List_Node is new S_Expression with record
>>     List : Lists.Vector;
>> end record;
>
> This sort of approach would work, though I don't much like it. There's
> no representation of a complete S-expression, just for the bits one is
> made up of.

Well technically, any S-expression node is also a full-fledged
S-expression. A subprogram taking any kind of node would look like:

procedure Make_Bar (From : S_Expression'Class);

> explicit discriminant is generally clearer.

Thinking about it, I start believing you're right.

> You could also make the explicit discriminant visible, eliminating the
> Is_Atom function, and declaring subtypes, which would eliminate the
> need for the explicit exceptions and tests. That might be a good idea.

Actually I find an enumerated discriminant clearer than a boolean one,
at least for that particular case.

However I'm still unsure about the pros and cons for having a public
discriminant rather than a private one.

>> Natacha
>
> So which is it, Natasha or Natacha?

They are both transliterations of Наташа, the former being English while
the latter is French. In an English context I consider both of them
equally valid, the first has a better integration in the English flow
while the latter is what is actually written on my ID.

Do I really have to pick one?


Thanks for your help,
Natasha