J3/10-168r1
To: J3
From: Malcolm Cohen
Subject: Interp on impure elemental functions.
Date: 2010 June 16

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NUMBER: F08/0018
TITLE: Impure elemental restrictions
KEYWORDS: IMPURE, ELEMENTAL
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION:

With the following two impure elemental procedures,
which perform essentially the same calculations,

  IMPURE ELEMENTAL SUBROUTINE one(x,y)
    INTENT(IN) x
    INTENT(OUT) y
    REAL :: z = 0
    y = x + z
    z = x
  END SUBROUTINE
  IMPURE ELEMENTAL REAL FUNCTION two(x,y)
    INTENT(IN) x
    INTENT(OUT) y
    REAL :: z = 0
    y = x + z
    z = x
    two = y - z
  END FUNCTION

consider these references:

  REAL a(10),b,c
  ...
  CALL one(b,a) ! (i) ok, equivalent to CALL one([(b,i=1,10)],a)
  CALL one(a,b) ! (ii) not ok, prohibited by 12.8.3p1, sentence 2.
  c = two(b,a)  ! (iii) ok, like (i)
  d = two(a,b)  ! (iv) NOT prohibited!?!

Was allowing case (iv) an oversight?

ANSWER:

Yes, this was an oversight: after adding impure elementals, the
elemental subroutine argument restrictions need to apply to elemental
functions as well.

EDITS to 10-007:

[314:7+] Insert new paragraph as follows.
  "In a reference to an elemental procedure, if any argument is an
   array, all actual arguments that correspond to INTENT (OUT) or
   INTENT (INOUT) dummy arguments shall be arrays.  All actual
   arguments shall be conformable."

[314:11-12] In 12.8.2, delete the third sentence; that sentence reads
            "For those ... conformable.".
{Redundant with new paragraph.}

[314:16-19] In 12.8.3, delete the second sentence; that sentence reads
            "In a reference ... conformable with them.".
{Redundant with new paragraph.}

NOTE: These edits subsume the one in the interp F08/0017 (10-167r1)
      "Elemental subroutine restrictions".

SUBMITTED BY: Malcolm Cohen

HISTORY: 10-168    m192  F08/0018 Submitted
         10-168r1  m192  Revised answer.

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