!standard 3.8(3)                                      19-01-10  AI12-0213-1/02
!standard 3.8(7)
!standard 3.8(8)
!standard 13.5.1(2)
!class Amendment 16-12-28
!status work item 16-12-28
!status received 16-10-06
!priority Very_Low
!difficulty Easy
!subject Unify record syntax
!summary

*** Missing.

!problem

Ada's record_type_definition and record_representation_clause are unique to the
language in that it is the only kind of type definition to feature an enclosed
list of components, and being that it is not a program unit or a named construct
such as a loop it was classically not considered relevant to allow an identfier
with its enclosing "end." However, many Ada users can attest to having records
with upwards of 15 or more components complete with comments and whitespace
leaving the enclosing "end record" to be below the page of start of the type
declaration - meaning some benefit would arise from being able to label the
"end record" with the type identifier.

!proposal

We propose introducing an "end record identifier" syntax for record
definitions (and thusly representation clauses) so that their syntax more
closely matches program units such as subprogram_declarations and
package_declarations. See the code segments below for an overview of the
proposed change:

   type Rec_B is record
      A : Boolean;
      B : Boolean;
   end record Rec_B;

   for Rec_B use record
      A at 0 range 0 .. 0;
      B at 0 range 1 .. 1;
   end record Rec_B;

As an alternative to:

   type Rec_B is record
      A : Boolean;
      B : Boolean;
   end record;

   for Rec_B use record
      A at 0 range 0 .. 0;
      B at 0 range 1 .. 1;
   end record;

Syntax

Here is what the BNF would look like for the proposed changes:

   record_definition ::=
      record
         component_list
      end record_terminator
      | null record

   record_terminator ::= record [record_identifier]

   record_representation_clause ::=
      for first_subtype_local_name use
         record [mod_clause]
            {component_clause}
         end record_representation_terminator;

   record_representation_terminator ::= record [first_subtype_local_name]

!wording

Replace 3.8(3)

record_definition ::=
   record
      component_list
   end record_terminator
   | null record

Add after 3.8(3)

record_terminator ::= record [record_identifier]

Add after 3.8(7)

The optional record_identifier within a given record_definition's
record_termintor must match the name of its enclosing type_declaration.

Replace 3.8(28)

    type Complex is
       record
          Re : Real := 0.0;
          Im : Real := 0.0;
       end record Complex;

Replace 13.5.1(2)

record_representation_clause ::=
   for first_subtype_local_name use
      record [mod_clause]
         {component_clause}
      end record_representation_terminator;

Add after 13.5.1(2)

record_representation_terminator ::= record [first_subtype_local_name]

!ASIS

[Not sure. Does ASIS expose the matching name at the end of a
construct?? - Editor.]

!ACATS test

An ACATS B-Test and C-Test are needed to check that the new capabilities are
supported.


!appendix

From: Justin Squirek
Sent: Wednesday, October 5, 2016  11:30 AM

I was considering amending my previous AI to be several (raise-when syntax
and a with-use clause), but after considering feedback I realized that these
would not blend well with the Ada language.

However, I do think proposing an AI on unifying record type declaration syntax
is worthwhile.

[This is version /01 of this AI, with a number of missing parts added. - Editor]

****************************************************************

From the minutes of the Lexington Meeting (October 2018):

Tucker suggests "end record <id>"; as an option, there is no interest in leaving
out the record. End by itself is disgusting.

Gary suggests that we would allow the name on end of the record representation
clause. Tucker argues against that, it doesn't declare anything. Others argue
that it could improve readability; it also would be consistent, otherwise you
would have to worry about the context of end record. We eventually agree that it
makes sense to allow it anywhere end record occurs.

The optional identifier has to match appropriately. Randy complains that a
record_definition (which is the construct with the end record) does not iteself
have an identifier. Rather, it is part of other constructs
(record_type_definition, record_extension) which themselves in turn are part of
a type_declaration, which is where the defining identifier comes from. So it is
not simple to describe the identifier that has to match. It should be possible
to describe this (perhaps by saying the "enclosing type_declaration"), we'll
leave it to the author to figure that out.

****************************************************************

From: Justin Squirek
Sent: Thursday, January 10, 2019  10:21 AM

Attached is my homework for AI12-0213-1-01, revised as per our discussions.
[This is version /02 - Editor.]

****************************************************************