Re: Real syntax problems in Ada

[Adam Beneschan <adam@irvine.com>]

On Tuesday, August 28, 2012 2:49:20 PM UTC-7, Randy Brukardt wrote:

> >> 2. "end record" instead of "end <record type name>";
> 
> >
> 
> >Yep, this is one I wish were different.  After working with Ada for about 
> >24 years
> > I still sometimes type in "end <type-name>" before I catch myself.

> I feel that way too, but there is a semantic reason why this isn't possible. 
> Specifically, the part after the "is" of a type declaration is a "type 
> definition". These are anonymous and can appear in various other contexts 
> (anonymous array and access types, for instance). The name of a type comes 
> from the type declaration, which is a separate semantic entity (and has 
> subtly different rules). I know that Janus/Ada processes "type definitions" 
> separately from the declarations, and thus including a name in the anonymous 
> part would be difficult to manage.
> 
> I once seriously looked at proposing allowing a name in a record type 
> declaration, and I couldn't figure out a reasonable way to do so given the 
> existing Ada semantics. Figuring out some way to hack the wording so that 
> the name associated with the declaration somehow can be matched in the 
> definition would seem to require changes all over the standard all out of 
> proportion to the size of the problem. So I don't think this is ever going 
> to happen.

Off the top of my head, it seems like you could modify 3.8 to allow "end <identifier>" in a record_type_definition, without saying anything in the Legality Rules (in 3.8) about the identifier.  Then, in 3.2.1, you can add a Legality Rule that if a full_type_declaration includes a record_type_definition, and the record_type_definition ends with "end <identifier>", then the identifier name must match the defining_identifier of the type declaration.  This would mean that if a record_type_definition is used anywhere else besides a full_type_declaration, then the identifier could be anything you want, which would be weird.  But that's not a real problem, since record_type_definition is used only in one place in the syntax.  It seems a little hacky since the Legality Rule would be in the wrong place, but I think it would work and wouldn't affect anything else in the RM.  

                             -- Adam