J3/01-297

Subject: Revised answer for Interp 86
From:    Malcolm Cohen
To:      J3
Date:    6th August 2001

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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.

(2) Not applicable.

(3) No, this was a mistake.

(4) Not applicable.

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: 00-292    m154  Submitted;  Passed by J3 meeting
         00-329    m155   Failed J3 letter ballot
         WG5/N1452 Added answer to questions 2 and 4.
         158-mjc-013 m158

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