J3/06-376r1

To: J3
From: Malcolm Cohen
Subject: NAMELIST, EQUIVALENCE, SAVE and BLOCK
Date: 2006/11/15

1. Introduction

This paper proposes fixing problems and confusions caused by the
potential use of NAMELIST, EQUIVALENCE, SAVE in BLOCK constructs.

2. Problems

For NAMELIST, there is a similar problem as for COMMON, in that
all the NAMELIST statements in a scoping unit contribute to that
namelist.  That is either confusing and hard to explain
(if the ones inside BLOCK don't) or error-prone and weird
(if they do).

Therefore, we should require that all the NAMELIST statements be
in the specification part of the subprogram, not inside any BLOCK.

Similar confusions arise for EQUIVALENCE, since the equivalence-sets
are glommed together from all the overlapping ones in a scoping unit.
Again, this would either be confusing and hard to explain, or
confusing and weird.  And since COMMON is not allowed in BLOCK, we
need to address EQUIVALENCE somehow otherwise we could extend the
COMMON in the BLOCK!

Slightly different problems arise for SAVE.  Certainly a global SAVE
should not be allowed in a BLOCK construct.  It would seem useful
to allow the SAVE attribute to be specified for individual BLOCK-local
variables, but the description of the SAVE attribute is currently
defective there.

3. Solutions

Prohibit NAMELIST from BLOCK.
Prohibit EQUIVALENCE from BLOCK.
Prohibit global SAVE from BLOCK.
Fix the description of the SAVE attribute to cover BLOCK entry/exit.

4. Edits

[97:17] "variable" -> "local variable of a program unit or subprogram"
{Exclude BLOCK-local variables from this definition.}

[97:19] after "local variable of a subprogram" insert "or BLOCK construct"
{Shared with all instances.}

[97:20] Append to paragraph
  "The SAVE attribute specifies that a local variable of a BLOCK construct
   retains its association status, allocation status, definition status, and
   value after termination of the construct unless it is a pointer and its target
   becomes undefined (16.5.2.2.3(4))."
{Mutated version for BLOCK-local variables.}

[177:21] Insert into list "NAMELIST statement, EQUIVALENCE statement,
            SAVE statement with no <saved-entity-list>"
{Prohibit these statements from appearing in a BLOCK construct.}

[177:21+] Insert new constraint
  "C8xx A SAVE statement in a BLOCK construct shall not specify a <common-block-name>."
===END===