To: J3                                                     J3/19-192r1
From:    Jon Steidel
Subject: RFI F18-014 OPERATION in REDUCE and CO_REDUCE
Date: 2019-August-05


Interpretation Request

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NUMBER: F18/014
TITLE: TYPE of OPERATION arguments to the REDUCE intrinsic
KEYWORDS: REDUCE, OPERATION, polymorphic, type
DEFECT TYPE: Erratum
STATUS: Submitted

QUESTION:

Section 16.9.161 REDUCE p3 describes the arguments to the intrinsic
subroutine CO_REDUCE.

The description of the ARRAY argument states:
 "ARRAY shall be an array of any type."

It describes the OPERATION argument as:

 "OPERATION shall be a pure function with exactly two arguments;
            each argument shall be a scalar, nonallocatable, non-
            pointer, nonoptional dummy data object with the same
            type and type parameters as ARRAY. If one argument has
            the ASYNCHRONUS, TARGET, or VALUE attribute, the other
            shall have that attribute.  Its result shall be a non-
            polymorphic scalar and have the same type and type
            parameters as ARRAY.  OPERATION should implement a
            mathematically associative operation.  It need not be
            commutative."

The function result of OPERATION cannot be polymorphic.  The arguments
to OPERATION must have the same type as its result, and thus cannot be
polymorphic.  However, ARRAY can be polymorphic.  This means the dynamic
type of ARRAY must be the same type as the arguments and result of
OPERATION.  This seems like an unfortunate requirement.

Was it intended that the dynamic type of ARRAY be required to match
the type and type parameters of the arguments of OPERATION?

ANSWER:

No, this requirement was not intended.  Edits are provided to correct
the problem.

EDITS:
[408:36] change "type and type parameters"
         to     "declared type and type parameters"

[408:39] change "type and type parameters"
         to     "declared type and type parameters"

so that the description of OPERATION reads:
  "shall be a pure function with exactly two arguments; each argument
   shall be a scalar, nonallocatable, nonpointer, nonoptional dummy
   data object with the same declared type and type parameters as ARRAY.
   If one argument has the ASYNCHRONOUS, TARGET, or VALUE attribute,
   the other shall have the attribute. Its result shall be a non-
   polymorphic scalar and have the same declared type and type
   parameters as ARRAY.  OPERATION should implement a mathematically
   associative operation. It need not be commutative."

[409:5] change "type and type parameters"
        to     "declared type and type parameters"

so that the first sentence of Result Characteristics reads:
  "The result is of the same declared type and type parameters as
   ARRAY."

SUBMITTED BY: Jon Steidel

HISTORY: F18-014   m219  Submitted

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