J3/06-240

Date: 31 July 2006
To: J3
From: Bill Long and John Reid
Subject: Issue 13 : co-array semantics
Reference: J3/06-007

Discussion of Issue 13 (page 89)

To address this comment, we propose that new bnf terms be introduced
to define <co-array-spec> and new sections be added at the end of
5.3.7 for the semantics. Some similar text is also needed for ALLOCATE.


Edits to J3/06-007

[62:16]. In C444, change '<deferred-shape-spec-list>' to
         '<deferred-co-shape-spec-list>'.

[89:4]. In C523, change '<deferred-shape-spec-list>' to
         '<deferred-co-shape-spec-list>'.

[89:13-14] Replace R511 by

    R511 <co-array-spec> <<is>> <deferred-co-shape-spec-list>
                         <<or>> <explicit-co-shape-spec>

[92:16+]. At the end of 5.3.7 add new subsections

    5.3.7.7 Allocatable co-array

    An <<allocatable co-array>> is a co-array that has the
    ALLOCATABLE attribute and a specified co-rank, but its co-bounds
    are determined by allocation or argument association.

    R518a <deferred-co-shape-spec> <<is>>   :

    C531a (R511) A co-array that has the ALLOCATABLE attribute shall have
          a <co-array-spec> that is a <deferred-co-shape-spec-list>.

    The co-rank of an allocatable co-array is equal to the number of colons in
    its <deferred-co-shape-spec-list>.

    The co-bounds of an unallocated allocatable co-array are undefined.
    No part of such a co-array shall be referenced or defined; however,
    the co-array may appear as an argument to an intrinsic inquiry function
    as specified in 13.1.

    The co-bounds of each co-dimension of an allocatable co-array are those
    specified when the co-array is allocated.

    The co-bounds of the allocatable co-array are unaffected by any
    subsequent redefinition or undefinition of variables on which the
    bounds' expressions depend.


    5.3.7.8 Explicit-co-shape co-array

    An <<explicit-co-shape co-array>> is declared with an
    <explicit-co-shape-spec>.

    R518b <explicit-co-shape-spec> <<is>>
                                   [[<lower-co-bound>:]<upper-co-bound>,]...
                                    [<lower-co-bound>:]*

    C531b (R511) A co-array that does not have the ALLOCATABLE attribute shall
          have a <co-array-spec> that is a <explicit-co-shape-spec>.

    The co-rank is equal to one plus the number of <upper-co-bound>s.

    R513      <lower-co-bound>     <<is>>   <specification-expr>

    R514      <upper-co-bound>     <<is>>   <specification-expr>

    C527 (R512) A <lower-co-bound> or <upper-co-bound> that is not an
          initialization expression shall appear only in a subprogram or
          interface body.

    If an explicit-shape co-array has co-bounds that are not initialization
    expressions, the co-bounds are determined at entry to the procedure by
    evaluating the co-bounds expressions. The co-bounds of such a co-array
    are unaffected by the redefinition or undefinition of any variable
    during execution of the procedure.

    The values of each lower-co-bound and upper-co-bound determine the
    co-bounds of the array along a particular co-dimension. The subscript
    range of the array in that co-dimension is the set of integer
    values between and including the lower and upper co-bounds. If the
    lower-bound is omitted, the default value is 1. The upper co-bound
    shall not be less than the lower co-bound.

[126:11]. After the end of the paragraph before NOTE 6.22, add pararaph:

     When an ALLOCATE statement is executed for a co-array, the values of
     the lower co-bound and upper co-bound expressions determine the co-bounds
     of the co-array. Subsequent redefinition or undefinition of any
     entities in the co-bound expressions do not affect the co-bounds.
     If the lower co-bound is omitted, the default value is 1. The upper
     co-bound shall not be less than the lower co-bound.