[J3] another PURE example

[Robert Corbett]

My first example program was
simpler.  Someone proposed a
solution to the problem as
shown in the first program that
does not work for the new
program.  I intend to include
both programs in my interp
request.

The key difference between the
programs is that the type
definition for the type of the
variable in the PURE subroutine
does not include the default
initialization.

Robert Corbett

> On Oct 6, 2020, at 9:45 AM, Brad Richardson via J3 <j3 at mailman.j3-fortran.org> wrote:
> 
> Am I missing something, or would the following simpler example be sufficient to demonstrate the problem?
> 
> MODULE V
>   REAL, TARGET :: X = 1.0
> END
> 
> MODULE PRINT
> USE V
> PRIVATE X
> CONTAINS
>   SUBROUTINE PRINTX
>     PRINT *, X
>   END
> END
> 
> MODULE T_M
>   TYPE T
>     REAL, POINTER :: P => X
>   END
> END
> 
> PURE SUBROUTINE SUBR
> USE T_M
>   TYPE(T) Y
>   Y%P = 2.0
> END
> 
> PROGRAM MAIN
> USE PRINT
>   CALL SUBR
>   CALL PRINTX
> END
> 
> Regards,
> Brad
> 
>> On Mon, 2020-10-05 at 22:12 +0000, Robert Corbett via J3 wrote:
>>       MODULE V
>>         REAL, TARGET :: X = 1.0
>>       END
>> 
>>       MODULE PRINT
>>       USE V
>>       PRIVATE X
>>       CONTAINS
>>         SUBROUTINE PRINTX
>>           PRINT *, X
>>         END SUBROUTINE PRINTX
>>       END
>> 
>>       MODULE T1
>>         TYPE T
>>           SEQUENCE
>>           REAL, POINTER :: P
>>         END TYPE T
>>       END
>> 
>>       MODULE T2
>>       USE V
>>       PRIVATE X
>>         TYPE T
>>           SEQUENCE
>>           REAL, POINTER :: P => X
>>         END TYPE T
>>       END
>> 
>>       PURE SUBROUTINE SUBR
>>       USE T1
>>       USE T2, TINIT => T
>>         TYPE(T) Y
>>         Y = TINIT()
>>         Y%P = 2.0
>>       END
>> 
>>       PROGRAM MAIN
>>       USE PRINT
>>         CALL SUBR
>>         CALL PRINTX
>>       END
>> ================================================================
>> 
>> I think the program above conforms to the Fortran 2018 standard,
>> but I am not able to check its conformance.  If anyone sees a
>> mistake in it, please let me know.
>> 
>> The program is another example of default initialization
>> breaking the assumptions that underlie the PURE attribute.
>> It shows that some of the fixes to the definition of PURE
>> that were proposed in response to my first example are
>> insufficient.
>> 
>> Because only one compiler was able to compile my first example,
>> I do not expect most compilers to be able to handle this
>> program.
>> 
>> I agree with Van that there are problems with the definition of
>> PURE that go back to the original definition of PURE.  Van also
>> asserted that the addition of type extensions made the problems
>> worse, but I do not understand what the additional problems
>> are.
>> 
>> Robert Corbett
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>> T
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