INTERFACE problem

[Richard E Maine]

On Mar 9, 2006, at 9:05 AM, Steve Kargl wrote:

> On Thu, Mar 09, 2006 at 09:34:22AM -0700, Michael Webb wrote:
>>
>> Module IntTest2
>>
>> IMPLICIT NONE
>>
>> CONTAINS
>>
>>      SUBROUTINE mytest(myfunc,x,s)
>>          INTERFACE
>>            FUNCTION myfunc(x,a,b)
>>               REAL(8)  x,a,b
>>            END FUNCTION myfunc
>>          END INTERFACE
>>
>>          REAL(8), INTENT(IN) :: x
>>          REAL(8), INTENT(OUT) ::  s
>>
>>          REAL(8)  a,b
>>
>>          s=myfunc(x,a,b)
>>
>>      END SUBROUTINE mytest
>>
>> END MODULE IntTest2
...
> With gfortran your code gives,
>
> troutmask:kargl[204] gfc -c f.f90
>  In file f.f90:7
>
>      SUBROUTINE mytest(myfunc,x,s)
>                             1
> Error: Symbol 'myfunc' at (1) has no IMPLICIT type

Then has someone submitted a bug report? :-) Because...

> In looking at your code, you need have used "IMPLICIT NONE"
> and you don't declare the return type form myfunc.  If
> you add "REAL(8) myfunc" to the interface, then gfortran
> compiles your code.

However implicit mappings are not inherited into interface bodies. See 
f95 [64:5-8], where this is discussed. Note the distinction made 
between different kinds of scoping units. For interface bodies, the 
default mapping does *NOT* come from the host. See also the comments in 
Note 5.24, which illustrates the distinction.

Therefore, the implicit none does not inherit into the interface body. 
The "usual" implicit mappings apply and the code is valid. It might not 
do what is intended because the implicit integer type seems odd here. 
And I would not recommend the coding style. But the standard allows it.

I personally think the exception for interface bodies was a mistake, 
but it was one intentionally done. Indeed, I recall the debate on the 
f90 interp that did this. It was at my very first J3 meeting, before I 
was a member, in 1991.

-- 
Richard Maine                |  Good judgment comes from experience;
Richard.Maine@nasa.gov       |  experience comes from bad judgment.
                             |        -- Mark Twain