J3/00-123

Date:     24th February 2000
To:       J3
From:     Malcolm Cohen
Subject:  Interpretation Request on ELEMENTAL procedures (revised)

NUMBER: 18 ?
TITLE: ELEMENTAL procedures with no arguments
KEYWORDS: Elemental, procedure
DEFECT TYPE:
STATUS:

Section 12.7.2 of IS 1539-1:1997 seems to assume there is at least one
argument to an elemental procedure.  The semantics of the following
examples do not seem to be clearly specified.

Example 1:
      ELEMENTAL INTEGER FUNCTION f()
        f = 0
      END

Example 2:
      ELEMENTAL INTEGER FUNCTION g(i,j)
        INTEGER,INTENT(IN) :: i,j
        g = i + j
      END

Example 3:
      ELEMENTAL INTEGER FUNCTION h2(i)
        INTEGER,INTENT(IN),OPTIONAL :: i
        h = i
      END

Example 4:
      ELEMENTAL SUBROUTINE s()
        REAL x,y,z
        x = 0
        y = 0
        z = x/y
      END

QUESTION 1:
What is the shape of a reference to function F in example 1?  Is it scalar?

QUESTION 2:
If G() is referenced as G(iscalar,jarray(1:0)), the result is a zero-sized
array.  Is "iscalar" referenced (need it be defined)?
Is the body of G() executed?

QUESTION 3:
What is the shape of a reference to H2() if the argument is textually
not present?

QUESTION 4:
When subroutine S is invoked, how many times is it executed?
Is this example standard-conforming, or may a processor raise a
divide-by-zero exception?

ANSWER:

(1) Yes, A reference to F() is scalar.
    Section 12.7.2 [214:28-29] says that
    "If the actual arguments are all scalar, the result is scalar."

(2) It is not possible to tell, in Fortran 95, whether the body of G() is
    executed, so that part of the question has no answer.
    [no edit required]
    Yes, ISCALAR must be defined; this is the same situation as writing
      ISCALAR + JARRAY(1:0)
    directly, with no user-defined ELEMENTAL procedure being used.
    [no edit required]

(3) If the I argument to H2 is textually absent, a reference to H2 returns a
    scalar result (cf. answer to question 1).  Note that execution of this
    procedure is not standard-conforming if the optional argument is not
    present.  The "H = I" line should be replaced by
      IF (PRESENT(I)) THEN
        H = I
      ELSE
        H = 0 ! or some other desired scalar value
      END IF
    [no edit required]

(4) The subroutine is executed once per invocation.  This is because any
    reference to the subroutine has no array arguments and so is not an
    "elemental reference" (section 12.4.3 [7-10]) but a normal subroutine
    reference.
    The example is not standard-conforming on a processor that does not
allow
    division by zero.
    [no edit required]

EDITS:

None.

SUBMITTED BY: Malcolm Cohen
HISTORY: 98-117 Submitted
         152-mjc-d Revised

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