J3/00-292
To: J3
From: Malcolm Cohen
Subject: Interpretation Request (F2002 unresolved issue 267)
Date: 17th September 2000

NUMBER: 000086
TITLE: Definition status requirements for defined operations
KEYWORDS: Defined operations
DEFECT TYPE:
STATUS: J3 consideration in progress

QUESTION:

7.1.7 "Evaluation of operations" states

  "This section applies to both intrinsic and defined operations.

   Any variable ... used as an operand in an expression shall be defined at the
   time the reference is executed."

(1) Was this particular requirement intended to apply to defined operations?
    I.e., is the following example program invalid:

      MODULE m
        INTERFACE OPERATOR (.cand.)
          MODULE PROCEDURE default_cand
         END INTERFACE
       CONTAINS
         LOGICAL FUNCTION default_cand(a,b) RESULT(r)
           LOGICAL,INTENT(IN) :: a,b
           IF (a) THEN
             r = b
           ELSE
             r = .FALSE.
           END IF
         END FUNCTION
       END
       PROGRAM example1
         USE m
         LOGICAL :: false = .FALSE.
         LOGICAL :: undefined
         PRINT *, false .cand. undefined
       END

(2) If the answer to the question is Yes (and the program is therefore
    invalid), would the program be standard-conforming if the penultimate line
    were changed to
        PRINT *, default_cand(false,undefined)
    ?

(3) 7.1.7 goes on to state
    "When a structure is referenced, all of the components shall be defined."
    Does this mean that pointer components must be associated with a defined
    target?  I.e. is the following program non-conforming?

       MODULE m2
         TYPE my_iptr
           PRIVATE
           INTEGER,POINTER :: ptr => NULL()
         END TYPE
         INTERFACE OPERATOR(.isnull.)
           MODULE PROCEDURE isnull_myip
         END INTERFACE
       CONTAINS
         LOGICAL FUNCTION isnull_myip(x)
           TYPE(my_iptr),INTENT(IN) :: x
           isnull_myip = ASSOCIATED(x%ptr)
         END FUNCTION
       END
       PROGRAM example2
         TYPE(my_iptr) a
         PRINT *,.isnull.a
       END

(4) If the program is not standard-conforming, would changing the penultimate
    line to
      "PRINT *,isnull_myip(a)"
    make it standard-conforming.

ANSWER:

(1) No, the requirement was not intentional.

(3) No, this was a mistake.

Discussion:

Usage of defined operations is intended to be equivalent to ordinary function
references.  All of the examples given above are standard-conforming.

EDITS:

[97:1] Replace "in an expression" with "of an intrinsic operation".
{Only require operands to be defined for intrinsic operations.}

[97:5] Replace "all of its components" with "it".
{A structure may be referenced whenever it is defined.}

HISTORY: 154-mjc-007  m154  Submitted

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