To: J3                                               J3/17-131r2
From: Dan Nagle & Malcolm Cohen
Date: 2017 February 16
Subject: repairs to reduce


During processing of 17-115, some issues with the OPERATION
argument of REDUCE were brought to subgroup's attention.
This paper attempts to repair these issues.

Specifically, it appears that the current description
of OPERATION does not mention several restrictions
that the OPERATION function must observe.

To work as intended, the result of OPERATION must be a scalar
to be combined with other array elements or partial results.

The arguments to OPERATION must have the same attributes,
since they will be different array elements of the same array,
or partial results of previous application(s) of OPERATION.

Since CO_REDUCE is just sitting there, language from it
is appropriated and used here, with minimal changes.  When doing so,
subgroup noticed that the name of the function argument
is "OPERATOR" in CO_REDUCE and "OPERATION" in REDUCE.
Subgroup prefers OPERATOR since it is an action noun.
However, this should be subject of a straw vote.

The Straw Vote results are that both procedures should have
the same name for the operation argument and that argument
should be named "OPERATION".  Edits to CO_REDUCE are included
to reflect this.


Edits to 17-007

[371:4-372:1-] 16.9.49 CO_REDUCE

change "OPERATOR" to "OPERATION" throughout

{make consistent with REDUCE}

[371:17-18] Same subclause, Arguments,
  Change "two scalar"
  to "exactly two arguments; each argument shall be a scalar".
  After "nonoptional" change "arguments of"
  to "dummy data objects with".
Making that sentence read
  "OPERATION shall be a pure function with exactly two arguments;
            each argument shall be a scalar, nonallocatable, nonpointer,
            nonpolymorphic, nonoptional dummy data object with the same
            type and type parameters as A."

[422:18-21] the current Arguments. OPERATION text:

"OPERATION shall be a pure function with two arguments
of the same type and type parameters as ARRAY. Its result shall have
the same type and type parameters as ARRAY. The arguments and result
shall not be polymorphic. OPERATION should implement a mathematically
associative operation. It need not be commutative."

[422:18] change "with two arguments"
to "with exactly two arguments; each argument shall be a scalar,
    nonallocatable, nonpointer, nonpolymorphic, nonoptional
    dummy data object"

[422:18-19] after "as ARRAY." add a sentence
"If one argument has the ASYNCHRONOUS, TARGET, or VALUE attribute,
the other shall have that attribute."

[422:19] change "Its result shall have"
to "Its result shall be a scalar and have"

The new Arguments. OPERATION text:

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

{make OPERATION actually work}