(j3.2006) resolving grammar ambiguities

[Bill Long]

Van Snyder wrote:
> On Sat, 2009-10-17 at 00:56 -0700, Robert Corbett wrote:
>> One of the members of Sun's Fortran team has been reviewing
>> the Fortran 2008 draft.  I have been able to answer most of
>> the questions he has raised, but tonight he raised one for
>> which I could not find an answer.
>>
>> Consider syntax rule R737 on page 158.  It is
>>
>>      data-target    is  variable
>>                     or  expr
>>
>> The syntax rule for variable is rule R602 on page 117.
>> It is
>>
>>      variable       is  designator
>>                     or  expr
>>
>> Thus, expr can be generated from data-target in two ways
>>
>>      data-target  ->  expr
>>
>> and
>>
>>      data-target  ->  variable  ->  expr
>>
>> If the second derivation is used, data-target is subject
>> to constraint C724, but if the first definition is used,
>> it is not.
> 
> I don't think there is a problem with the constraints, since C602
> requires <expr> to be a reference to a function that returns a pointer.

And the corresponding C726 requires that <expr> be a reference to a 
function that returns a data pointer.  Not quite a match.  If C602 said 
"data pointer" instead of just "pointer", then the <expr> part of 
<data-target> could be cleanly dropped, as C726 would be redundant.

Cheers,
Bill


> 
> The "or expr" part of R737 is unnecessary, but harmless, since the
> second derivation arrives at the same syntax, with the constraint that
> <expr> is a reference to a function that returns a pointer.  Applying
> C724 to the second derivation just says "<variable> has to have the
> POINTER attribute" and then C602 says "and by the way, <expr> has to be
> a reference to a function that returns a pointer."  It doesn't hurt
> anything to say it twice.
> 
>> I could find no explanation of how such ambiguities should
>> be resolved.
>>
>> Bob Corbett
>> _______________________________________________
>> J3 mailing list
>> J3 at j3-fortran.org
>> http://j3-fortran.org/mailman/listinfo/j3
> 
> _______________________________________________
> J3 mailing list
> J3 at j3-fortran.org
> http://j3-fortran.org/mailman/listinfo/j3

-- 
Bill Long                                   longb at cray.com
Fortran Technical Support    &              voice: 651-605-9024
Bioinformatics Software Development         fax:   651-605-9142
Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120