To:         J3 Members                                       J3/17-184
From:       Van Snyder
Subject:    Implicit declaration and BLOCK constructs
References: 17-007r2
Date: 2017 July 28

1. Discussion
=============

Subclause 8.7p4 says that if a variable in a BLOCK construct is not
explicitly declared in a type declaration statement, and the outermost
inclusive scope is not a type definition, the effect is as if it were
explicitly declared in the outermost inclusive scope in which it
appears, which (according to the definition of inclusive scope) would
apparently not be the BLOCK construct.

Subclause 19.4p1 says that an entity that is explicitly declared in the
specification part of a BLOCK construct, other than only in ASYNCHRONOUS
and VOLATILE statements, is a construct entity.  19.4p1 does not
restrict the declaration to type declaration statements.

At least three processors accept the following and appear to agree that
the variable R in each block is a construct entity, in that they print
different values for their shapes:

program P

  block
    dimension R(3)
    print '(a,i0)', 'Shape(R) = ', shape(r)
  end block

  block
    dimension R(2,2)
    print '(a,2(1x,i0))', 'Shape(R) = ', shape(r)
  end block

end program P

Shape(R) = 3
Shape(R) = 2 2

It is clear that they do not consider R to be declared as two arrays
with different ranks in the inclusive scope of the BLOCK constructs.  It
cannot be determined (except maybe by looking at generated code) whether
they declared a scalar named R in the inclusive scope.

Subclauses 8.7p4 and 19.4p1 ought to be consistent.  So as not to
require changes to the three processors that behave as above, the scope
of declaration specified in 8.7p4 ought to be the outermost scope
containing the object if it is declared in any statement, not the
outermost inclusive scope.  Since it is apparently not possible to
detect whether a variable that is not explicitly declared in any
statement within a BLOCK construct is or is not a construct entity, it
would be simpler if variables either explicitly or implicitly declared
in BLOCK constructs were construct entities, except those accessed by
host association and declared only in ASYNCHRONOUS or VOLATILE
statements.

In

  program Q

    block
      asynchronous :: A
    end block

  end program Q

subclause 19.4p1 says that A is not a construct entity.  According to
(currently defective) 8.7p4, A is declared in the scope of program Q,
which is inconsistent with declarations of R in program P above.  To
make it clear that A is a construct entity, the description of
ASYNCHRONOUS and VOLATILE in 19.4p1 should explicitly apply only to
entities accessed by host association.

2. Edits
========

[121:7 8.7p4 IMPLICIT statement] Delete "inclusive".

[516:12 19.4p1 Statement and construct entities] After "explicitly" with
"explicitly or implicitly".  In light of 8.7p4 saying "as if ...
explicitly" this might not be necessary.

[516:13 19.4p1 Statement and construct entities] Replace "only in
ASYNCHRONOUS and VOLATILE" with "one accessed by host association and
declared only in ASYNCHRONOUS or VOLATILE".