Version 1.1.1.1 of ais/ai-00064.txt

!section 3.11(9)
!section 8.5.4(1)
!subject Renaming-as-body and elaboration
!reference RM95 3.11(9,10)
!reference RM95 8.5.4(1)
!from Tucker Taft 95-07-05
!reference as: 95-5208.a Tucker Taft 95-7-5>>
!discussion

In 3.11(10), it indicates that an elaboration check is only
required when a subprogram has an explicit body that is a
subprogram_body.  However, when a renaming declaration is
used as a body, it is possible for the elaboration of the
renaming declaration to require the evaluation of a name,
such as X.all, that implies some sort of elaboration check
should be performed.  For example:

    function F return Integer;
    type Pointer_To_Func is access function return Integer;

    X : Pointer_To_Func := Q'Access;  -- Presume Q already elaborated

    Y : Integer := F;  -- We need some sort of elaboration check

  ....

    Z : Pointer_To_Func := X;

    function F return Integer renames Z.all;

In the above, clearly we need to wait until "Z.all" is elaborated
before calling F.  However, it is not clear that any
check for this is required by 3.11(10).

It seems that the right model for renaming-as-body that
occurs after the subprogram is frozen should be that of a wrapper
subprogram, with its own elaboration "bit."

By the way, where is "body" defined?  It presumably includes
entry body, and perhaps renaming-as-body.  However, only the
syntactic entity BODY is defined (in 3.11).  Where is the
unbolded term "body" defined?

-Tuck

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!section 03.11(09)
!subject Call for letter ballot on AI95-00064
!reference AI95-00064/01
!from Norman Cohen 96-04-29
!reference 96-5524.a Norman H. Cohen 96-4-29>>
!discussion

I call for a letter ballot on AI-64 because I believe the elaboration
check needs to be defined more precisely:  Presumably, it is checked
both that the renaming declaration has been elaborated and that the
body of the renamed subprogram has been elaborated.  (In addition, the
AI should make it obvious that this check is performed at the time of a
call.)

I suggest that the !recommendation be rewritten in
language that parallels 3.11(10) and 3.11(14):

   For a call to a (non-protected) subprogram that has a
   renaming-as-body, a check is made that the renaming declaration has
   already been elaborated, and that the body of the subprogram named in
   the renaming declaration has already been elaborated.  This check and
   the evaluations of any actual parameters of the call are done in an
   arbitrary order.  The exception Program_Error is raised if this check
   fails.

(Perhaps just the first sentence will suffice as the !summary.)

Can this be considered an editorial correction, and a revised version
recirculated for letter ballot, before the next meeting?

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!section 3.11(09)
!subject Call for letter ballot on AI95-00064
!reference 03.11(09)
!reference AI95-00064/01
!reference 96-5524.a Norman Cohen 96-04-29
!reference 96-5543.a Robert A Duff 96-5-8>>
!discussion

Norman says:

> I call for a letter ballot on AI-64 because I believe the elaboration
> check needs to be defined more precisely:  Presumably, it is checked
> both that the renaming declaration has been elaborated and that the
> body of the renamed subprogram has been elaborated.  (In addition, the
> AI should make it obvious that this check is performed at the time of a
> call.)
> 
> I suggest that the !recommendation be rewritten in
> language that parallels 3.11(10) and 3.11(14):
> 
>    For a call to a (non-protected) subprogram that has a
>    renaming-as-body, a check is made that the renaming declaration has
>    already been elaborated, and that the body of the subprogram named in
>    the renaming declaration has already been elaborated.  This check and
>    the evaluations of any actual parameters of the call are done in an
>    arbitrary order.  The exception Program_Error is raised if this check
>    fails.
> 
> (Perhaps just the first sentence will suffice as the !summary.)

I agree with Norm's complaint.  However, I think the above wording fails
to handle the transitive cases.  If the body of P renames Q, and the
body of Q renames R, and the body of R renames S, then we need to check
that the bodies of all of P, Q, R, and S have been elaborated.  The
above wording only checks P and Q.

I think a better solution is to add something like this to the !wording
section:

  Add a paragraph before 8.5.4(8) to define the run-time semantics of
  renamings-as-body:

      The execution of a renaming-as-body is equivalent to the execution
      of a subprogram_body that simply calls the renamed subprogram
      with the same parameters.

This makes the rule correctly transitive, and I think is more elegant
anyway.

> Can this be considered an editorial correction, and a revised version
> recirculated for letter ballot, before the next meeting?

Will do.

By the way, I disagree that the !summary needs to be so precise.
Everybody knows that elaboration checks are done at call sites, and the
summary is supposed to be as simple as possible without being outright
wrong.

The !wording section, on the other hand, defines the precise rule (or it
will, soon).  (This is one AI that I thought was subtle enough that it
deserved to have a wording section.)  So, Norm, I suggest you read the
new !wording when I send it out, and criticize *that* if you think it's
still not right.

- Bob


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