J3/13-312
To: J3
From: Van Snyder
Subject: Specifications for US-08 -- explicit specification of EXTERNAL
Date: 2013 August 21
Reference: 13-244r1

1. Requirements
---------------

From 13-244r1:

  Currently, there is no way to require explicit specification of the
  external attribute.  Providing such a means would aid program
  checking.

2. Specification
----------------

Provide a new statement or an annotation or variation of an existing
statement that requires explicit declaration of the EXTERNAL attribute.
If it appears in a scoping unit, it applies in nested scoping units
(BLOCK constructs and internal or module procedures).

This is independent from requiring explicit interface for external
procedures, which is not required by this work item.

3. Syntax
---------

There is as yet no consensus concerning syntax.  Several proposals have
been:

  IMPLICIT NOEXTERNAL
  IMPLICIT, EXTERNAL :: NONE
  EXTERNAL, NOIMPLICIT
  NO IMPLICIT EXTERNAL
  EXTERNAL, EXPLICIT
  EXPLICIT[,] EXTERNAL

4. Edits
--------

None yet.  Assuming it's a new statement, not a variation on an existing
statement, edits might be something along the lines of

[Introduction p2+] In the new list of new features, insert a list item:

" o Programs and procedures:
    An XXX statement can require explicit declaration of the EXTERNAL
    attribute.
"

[10-007r1:287:4-] Insert a subclause

"12.4.3.5a XXX statement

The XXX statement specifies that the EXTERNAL attribute (5.3.9) shall be
explicitly declared.

R1210a <xxx-stmt> <<is>> XXX

C1215a (R1210a) If an XXX statement appears within a scoping unit, a
       <procedure-name> that is a <procedure-designator> in a
       <function-reference> or <call-stmt> in that scoping unit, or
       within a BLOCK construct or procedure within that scoping unit,
       shall be explicitly declared to have the EXTERNAL attribute
       (5.3.9) by a type declaration statement, interface body
       (12.4.3.2), EXTERNAL statement (12.4.3.5), or procedure
       declaration statement (12.4.3.6).

C1215b (R1210a) An XXX statement shall not appear in a BLOCK DATA
       program unit.
"