To: J3                                                     J3/21-138
From: Van Snyder
Subject: Interp F18/nnn Access Internal Procedure in Interface Body
Reference: 18-007r1
Date: 2021-May-03

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NUMBER: F18/nnn
TITLE: Access Internal Procedure in Interface Body
DEFECT TYPE: TBD
STATUS: TBD

EXAMPLE:

Consider:

      program Test_Internal

        interface
          subroutine S1 ( S )
            import S2
            procedure ( S2 ) :: S
          end subroutine S1
        end interface

      contains

        subroutine S2
        end subroutine S2

      end program Test_Internal

C897  (R867) Each <import-name> shall be the name of an entity in the
      host scoping unit.

S2 satisfies this constraint. It is in the host scoping unit.

C8101 Within an interface body, an entity that is accessed by host
      association shall be accessible by host or use association within
      the host scoping unit, or explicitly declared prior to the
      interface body.

S2 violates this constraint. It is not, and cannot be, declared before
the interface block.

Some processors accept the program, and others do not. Interestingly, if a
procedure declaration (with or without the POINTER attribute) that uses
the internal subroutine to specify its interface appears before the
interface block, e.g.,

      procedure ( s2 ), pointer :: P

the processor that rejects the program then accepts it. This is not a
declaration of S2 that precedes the interface block.

QUESTION:

Unlike Pascal, Fortran does not have a FORWARD declaration. It is
therefore impossible to declare an internal subprogram before an
interface block in the host scoping unit.

Was it intended that it be impossible to use an internal subprogram to
specify the interface of a dummy procedure in an interface body?

ANSWER 1:

This was intended.

ANSWER 2:

This was an oversight.

EDITS 1:

No edits are necessary.

EDITS 2:

Revise constraint C8101

C8101 Within an interface body, an entity that is accessed by host
      association shall be accessible by host or use association within
      the host scoping unit, explicitly declared prior to the
      interface body, or an internal procedure of the host scoping unit.

SUBMITTED BY: Van Snyder

HISTORY: 21-138   m224  Submitted

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