To: J3                                                     J3/17-253r1
From: Robert Corbett
Subject: IMPORT statements in BLOCK constructs
Date: 2017 October 19
Reference: 17-007r2

1. Discussion

The specification of the IMPORT statement in subclause 8.8 of
17-007r2 describes the semantics of IMPORT statements in terms
of their effects on host association.  Host association does not
apply to entities in BLOCK constructs.  The mechanism for accessing
entities in enclosing scoping units from within BLOCK constructs is
inclusive scoping, not host association.  As currently described,
IMPORT statements have no effect on BLOCK constructs.

For example, consider the program

      PROGRAM MAIN
        IMPLICIT NONE
        REAL :: X = 1.0
        A: BLOCK
          IMPORT, NONE
          PRINT *, X
        END BLOCK A
      END


According to subclause 8.8p2, the statement IMPORT, NONE specifies
that no entities in the host scoping unit of BLOCK A are made
accessible within BLOCK A by host association.  However, because
the scope of the variable X includes BLOCK A, the variable X is
accessible within BLOCK A.  Therefore, the program is conformant.
Users might be surprised that the statement IMPORT, NONE leaves
the variable X accessible in the BLOCK construct.

Edits are provided to make the semantics of IMPORT statements
work for BLOCK constructs.  A note has been added illustrating a
tricky case.


2. Edits to 17-007r2

[123:19] 8.8 IMPORT statement, p1
         Insert " other than a BLOCK construct" between
         "in a scoping unit" and ", an entity".
{The resulting sentence is "If the ONLY specifier appears on an
 IMPORT statement in a scoping unit other than a BLOCK construct,
 an entity is only accessible by host association if its name
 appears as an <import-name> in that scoping unit.".}

[123:20] 8.8 IMPORT statement, p1
         Insert
         "If a BLOCK construct contains one or more IMPORT
          statements with ONLY specifiers, identifiers of local
          and construct entities in the host scoping unit that are
          not in the <import-name-list> of at least one of the
          IMPORT statements are inaccessible in the BLOCK
          construct."
         after "that scoping unit".

[123:23] 8.8 IMPORT statement, p2
         Insert
         "An IMPORT, NONE statement in a BLOCK construct specifies
          that the identifiers of local and construct entities in
          the host scoping unit are inaccessible in the BLOCK
          construct."
         after "procedure."

[123:25] 8.8 IMPORT statement, p3
         Delete "by host association"
{The resulting sentence is "An IMPORT, ALL statement in a scoping
 unit specifies that all entities from the host scoping unit are
 accessible in that scoping unit."}

[123:30-31] 8.8 IMPORT statement, p5
         Replace "in a scoping unit ... host association." with
         "in a scoping unit other than a BLOCK construct, each
          entity named in the list is accessible.".
{The resulting sentence is "If an IMPORT statement with an
 <import-name-list> appears in a scoping unit other than a
 BLOCK construct, each entity named in the list is accessible."}

[124]    8.8 IMPORT statement, after NOTE 8.44
         Insert
         "NOTE 8.44a
          The program

            PROGRAM MAIN
              BLOCK
                IMPORT, NONE
                !IMPORT, ONLY: X
                X = 1.0
              END BLOCK
            END

          is not conformant.  The variable X is implicitly
          declared in the scoping unit of the main program.
          The statement IMPORT, NONE makes X inaccessible in
          the BLOCK construct.  If the IMPORT, NONE statement
          is replaced with the IMPORT statement in the comment,
          the program is conformant."

[513:9]  19.1 Scopes, identifiers, and entities
         Insert
         ", or where an IMPORT statement (8.8) makes the
          identifier inaccessible"
         after "(19.3, 19.4)" and before the full stop.
{19.3 refers to the subclause titled "Local identifiers".}
{19.4 refers to the subclause titled "Statement and construct
 entities".}