J3/13-245
To: J3
From: Malcolm Cohen
Subject: Interp F03/0064
Date: 2013 February 13

----------------------------------------------------------------------

NUMBER: F03/0064
TITLE: Recursive declaration of procedure interfaces
KEYWORDS: procedure, interface
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION:

Q1. Consider the following program:

      PROGRAM foo
        PROCEDURE(sub) :: p
        INTERFACE
          SUBROUTINE sub(p2)
            IMPORT p
            PROCEDURE(p) :: p2
          END SUBROUTINE
        END INTERFACE
      END PROGRAM

C1216 appears to prohibit the case of an interface name in a procedure
declaration statement being the name of something declared in a later
procedure declaration statement.  But it does not appear to prohibit
the case of an interface name being the name of something declared in
a later interface body.

In the above program, the characteristics of p rely on the
characteristics of sub.  The characteristics of sub, in turn, rely on
the characteristics of p.

Is this program standard-conforming?

Q2. Consider the module

    MODULE m1
    CONTAINS
      SUBROUTINE s(p)
        PROCEDURE(s) :: p
      END SUBROUTINE
    END MODULE

Constraint C1216 does not apply here since "s" is not declared by a
procedure declaration statement; unlike Q1, it is also not declared by
an interface body.  However, the characteristics of S have not been
determined before the procedure declaration statement has been
processed, and that cannot be processed until we know what the
interface of S is.

Is this program unit standard-conforming?

Q3. Consider the module

    MODULE m2
    CONTAINS
      SUBROUTINE s1(a)
        PROCEDURE(s2) :: a
      END SUBROUTINE
      SUBROUTINE s2(b)
        PROCEDURE(s1) :: b
      END SUBROUTINE
    END MODULE

The interface of A depends on the interface of S2, which depends on
the characteristics of B, which depends on the characteristics of S1,
which depends on the characteristics of A; a circular dependency.

Is this program unit standard-conforming?

Q4. Consider

      MODULE m3
        PROCEDURE(s),POINTER :: sptr
      CONTAINS
        SUBROUTINE s(p)
          PROCEDURE(sptr) :: p
        END SUBROUTINE
      END MODULE

In the normal course of events there is no problem declaring a
procedure pointer to have the interface of a module procedure that is
defined later, and this is desirable, but in this case there seems to
be a circular dependency between the characteristics of sptr, s, and
p.

Is this program unit standard-conforming?

ANSWER:

None of the examples are standard-conforming, as the standard does not
establish an interpretation for them.

An edit is provided to clarify this.

EDIT to 10-007r1:

[288:3] 12.4.3.6p2, append new sentence
  "The interface specified by <interface-name> shall not depend on any
   characteristic of a procedure identified by a
   <procedure-entity-name> in the <proc-decl-list> of the same
   procedure declaration statement."

SUBMITTED BY: Rob James

HISTORY: 05-179    m172  F03/0064 submitted
         05-226    m173  Passed by J3 meeting
         06-133    m175  Failed J3 letter ballot #12
         09-149    m187  Passed by J3 meeting
         09-187r2  m188  Failed J3 letter ballot #18 09-155
         13-nnn    m200  Revised

----------------------------------------------------------------------