J3/13-216

To: J3
From: Van Snyder
Subject: Array as bounds specification for explicit-shape array
Date: 2013 December 19
Reference: 04-136, 04-196; 2004 hate-dislike-like-love score 0-0-11-1

Title: Array as bounds specification for explicit-shape array

Submitted by: Van Snyder

Status: For consideration

Basic functionality: Allow a rank-one explicit-shape array with constant
shape as a bounds specification for an explicit-shape array.

Rationale: For arrays with more than a few dimensions, it is tedious to
specify their bounds in specification expressions individually if they
are available as an array.  One example is where they are the bounds of
other arrays.  It is impossible, not tedious, if all the bounds are
calculated by one function reference and returned as an array, because
function results cannot be subscripted.

Estimated impact: Minor

Markham M6 conformance: Remove simple deficiency and discrepancy.

Detailed specification: Allow a rank-one explicit-shape array with
constant shape as a bounds specification for an explicit-shape array.
The rank of the declared array is the extent of the bounds array.

Draft edits: To estimate scope of project

Add an alternative to R515

R515 <array-spec> <<is>> <explicit-shape-spec-list>
                  <<or>> <array-explicit-shape-spec>
                  <<or>> ...

Add definition of <array-explicit-shape-spec> to 5.3.8.2, near C531:

R518a <array-explicit-shape-spec> <<is>> [ <array-lower-bound> : ]
                                         <array-upper-bound>

R518b <array-lower-bound> <<is>> <int-expr>

R518c <array-upper-bound> <<is>> <int-expr>

C531a (R518a) If <array-lower-bound> does not appear,
      <array-upper-bound> shall be a rank-one constant-extent array.

C531b (R518a) If both <array-lower-bound> and <array-upper-bound>
      appear, either one or both shall be rank-one constant-extent
      arrays, and their shapes shall conform.

C531c (R518a) Each <array-lower-bound> and <array-upper-bound> shall be
      (1) a specification expression,
      (2) an array constructor with elements that are specification
          expressions and every <ac-implied-do-control> is a constant
          expression, or
      (3) a reference to a standard intrinsic function other than NULL,
          or a specification function, with arguments that are
          specification expressions.

An array is a constant-extent array if its bounds are constant
expressions.

Split 5.3.8.2p3 into 5.3.8.2p3 and 5.3.8.2p5 after "lower bound is 1".

Add a paragraph 5.3.8.2p4 between those separated paragraphs:

The values of <array-lower-bound> and <array-upper-bound> determine the
bounds, and hence the extents, of all dimensions of an array.  If
<array-lower-bound> appears it specifies the lower bounds; otherwise the
lower bound of every dimension is 1.  The rank of the array is the
extent of <array-upper-bound> if it is an array, and <array-lower-bound>
otherwise.

Add a note at the end of 5.3.8.2:

NOTE 5.12a
  Example of <array-explicit-shape-spec>:
    SUBROUTINE EXA ( A )
      REAL, INTENT(INOUT) :: A(:,:,:,:)
      REAL :: B(SHAPE(A)), C(FINDLOC(A,42))
  The array B is an automatic array that has the same shape as A.
  The array C is an automatic array that has a shape determined by the
  first occurrence in array-element order of 42 in the array A.