To: J3                                                       J3/16-158
From: Van Snyder
Subject: Problems with constraints on IMPLICIT NONE
Date: 2016 February 03
Reference: 16-007

1. Introduction
===============

The constraints on the IMPLICIT statement have the effect of prohibiting

  IMPLICIT NONE
  IMPLICIT NONE ( EXTERNAL )

or

  IMPLICIT NONE ( TYPE )
  IMPLICIT NONE ( EXTERNAL )

or

  IMPLICIT DOUBLE PRECISION ( D, Z )
  IMPLICIT NONE ( EXTERNAL )

We probably did not intend this.

2. Edits
========

[113:14-18 C590 C591] Replace constraints C590 and C591:

"C590 (R563) If IMPLICIT NONE with an <implicit-none-spec> of TYPE, or
      IMPLICIT NONE without an <implicit-none-spec-list>, appears in a
      scoping unit, it shall precede any PARAMETER statements that
      appear in the scoping unit, and an IMPLICIT statement with
      <implicit-spec-list> shall not appear.

"C590a (R563) IMPLICIT NONE without an <implicit-none-spec-list> shall
      not appear more than once in a scoping unit.

"C590b (R563) IMPLICIT NONE with an <implicit-none-spec-list> of TYPE
      shall not appear more than once in a scoping unit.

"C591 (R563) IMPLICIT NONE with an <implicit-none-spec> of TYPE and
      IMPLICIT NONE without an <implicit-none-spec-list> shall not
      both appear in the same scoping unit."

3. Questions without answers
============================

Do we want to add most of the text of C593 to the introductory waffle in
5.7p1?

Do the IMPLICIT specifications in a module or submodule apply to its
submodules where there are no IMPLICIT specifications?  We don't say so
in 5.7 or 11.2.3.  Either way, we could probably fit this into C593 and
5.7p3.  Does this need an interp?