J3/10-195
To: J3
From: Malcolm Cohen
Subject: Interp on vector subscripts
Date: 2010 June 16

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NUMBER: F08/0039
TITLE: Many-one vector subscript usage.
KEYWORDS: Vector subscripts.
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION:

Consider
  SUBROUTINE zap(z,i)
    REAL z(:)
    INTEGER i(:)
    IF (no_duplicates(i)) z(i) = 0
  END SUBROUTINE
  ...
  REAL x(10)
  ...
  CALL zap(x,(/ 2,3,2 /))

(The user-defined function no_duplicates returns .TRUE. if and only if
 its argument has no duplicate values.)

6.5.3.3.2 "Vector subscript" paragraph 3 says:
  "If a vector subscript has two or more elements with the same value,
   an array section with that vector subscript shall not appear in a
   variable definition context (16.6.7)."

In the execution of zap from the CALL statement, the array section
z(i) has a vector subscript with two elements with the same value, and
appears in a variable definition context, in violation of the stated
requirement.

Q. Is this program fragment standard-conforming?

ANSWER:

Yes, this program is standard-conforming.  The quoted requirement is
poorly worded; an edit is supplied to correct it.

EDITS to 10-007:

[124:9] Replace "shall ... (16.6.7)" with
  "is not definable and shall not be defined or become undefined".

SUBMITTED BY: Malcolm Cohen

HISTORY: 10-195   m192 F08/0039 Submitted

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