J3/14-128r1
To: J3
From: Robert Corbett
Subject: making WHERE obsolescent
Date: 2014 February 13

Proposal:
I propose that WHERE constructs and WHERE statements be made
obsolescent in the next standard.

Syntax and specifications:
The syntax and specifications are unchanged, except that
conforming processors will be required to diagnose the
newly obsolescent feature.

Rationale:
Like FORALL constructs and statements, WHERE constructs and
statement have failed to facilitate parallel programming.  WHERE
constructs and statements are difficult to understand and
difficult to implement.  The benefits offered by WHERE constructs
and statements have proved to be too meager to justify their
inclusion in the Fortran standard.  Therefore, WHERE constructs
and statements should be made obsolescent.

The functionality of WHERE constructs and statements can be
emulated using DO CONCURRENT constructs.

Unlike FORALL constructs and FORALL statements, there are few
references to the text that describes WHERE constructs and
statements outside of the subclause that describes them
(Clause 7.2.3).  The changes needed to the standard to make
WHERE constructs and statements obsolescent are limited,
consisting mainly of the noting their changed status in the
Introduction, the Deleted and Obsolescent Features clause
(Clause 1.7) and the Obsolescent Features portion of Annex B,
and changing the font of Clause 7.2.3 to obsolescent font.
A few additional changes are needed, perhaps the most annoying
of which is that the list of branch target statements in
Clause 8.2.1 needs to be reordered to make the list correct
when the obsolescent text is ignored.