To: J3                                                     J3/21-150
From: Malcolm Cohen
Subject: Interp F18/030 CO_REDUCE OPERATION with coarray arg
Date: 2021-June-20

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NUMBER: F18/030
TITLE: CO_REDUCE/REDUCE OPERATION with coarray argument
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION:

Consider the function

  Pure Real Function f(a,b) Result(r)
    Real,Intent(In) :: a[*],b[*]
    r = a[1]*b[1]
  End Function

This function appears to satisfy all the requirements on the OPERATION
argument to CO_REDUCE.

Q1. Was this intended to be a valid operation for CO_REDUCE?

Q2. Was this intended to be a valid operation for REDUCE?

ANSWER:

A1. No, this was not intended to be valid; the arguments of OPERATION
    should not have been permitted to be coarrays.

A2. Likewise, this was not intended to be valid.

Edits are supplied to correct this oversight.

EDIT to 18-007r1:

[357:9] 16.9.49 CO_REDUCE, p3 Arguments, OPERATION argument,
        After "nonallocatable," insert "noncoarray,".
        That makes the first sentence of the argument read:
"OPERATION shall be a pure function with exactly two arguments; the
           result and each argument shall be a scalar, nonallocatable,
           noncoarray, nonpointer, nonpolymorphic data object with the
           same type and type parameters as A."
{The "noncoarray" requirement is superfluous for the result,
 but that is not harmful.}

[408:36] 16.9.161 REDUCE, p3 Arguments, OPERATION argument,
         Before "nonpointer," insert "noncoarray,".
         That makes the first sentence of the argument read:
  "OPERATION shall be a pure function with exactly two arguments; each
             argument shall be a scalar, nonallocatable, noncoarray,
             nonpointer, nonpolymorphic, nonoptional dummy data object
             with the same type and type parameters as ARRAY."
{It is "interesting" that these two very similar requirements are
 being expressed differently. Perhaps there is a good reason.}

SUBMITTED BY: Malcolm Cohen

HISTORY: 21-nnn   m224  Submitted

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