To: J3                                                     J3/18-242
From:    Van Snyder
Subject: Irregularities (index variables)
Date: 2018-September-13

Introduction
============

To reduce surprises, especially for newcomers to (modern) Fortran, it
would be helpful if facilities that have similar purposes had similar
details.

The example under attention here is index variables.

In <ac-implied-do-control>, the <ac-do-variable> can be preceded by
<integer-type-spec> ::.

In <data-implied-do>, the <data-i-do-variable> can be preceded by
<integer-type-spec> ::.

In <concurrent-header>, the <concurrent-control-list> can be preceded by
<integer-type-spec> ::.

This is not possible in <loop-control> or <io-implied-do>.

Proposal
========

To eliminate this irregularity

(1) <integer-type-spec> :: should be allowed before the <do-variable> in
    <loop-control>, with the additional effect that the <do-variable>
    becomes a construct entity.  Because a <do-variable> with
    <integer-type-spec> :: is a construct entity, there would be no harm
    to allow it to have the same name as the <do-variable> of an
    enclosing DO construct.

(2) <integer-type-spec> :: should be allowed before the <do-variable> in
    <io-implied-do-control>, with the additional effect that the
    <do-variable> becomes a statement entity.  Because there might be
    more than one <do-variable> within the same statement, and there is
    no concept of "the scope of an <io-implied-do>," a <do-variable>
    with <integer-type-spec> :: should probably not be allowed to have
    the same name as the <do-variable> of an enclosing <io-implied-do>.

Use Cases
=========

I think this is too bleeding obvious to need explicitly described use
cases.