To: J3                                                     J3/26-203
From: Malcolm Cohen
Subject: Interp F23/024 on coindexing and SIMPLE procedures
Date: 2026-October-16


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NUMBER: F23/024
TITLE: May a simple procedure depend on variables on other images?
KEYWORDS: coarray, coindexed, SIMPLE
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress
REFERENCES: 24-007

QUESTION:

Consider

    REAL SIMPLE FUNCTION f(x)
        REAL,INTENT(IN) :: x[*]
        f = x[Mod(This_Image(),Num_Images())+1]
    END FUNCTION

This function depends on the value of a variable on another image when
the number of images is greater than one. A variable on another image
is the very epitome of a nonlocal variable.

Just as a pure procedure is forbidden to write to a variable that
could be on another image (C15104), surely a simple procedure should
be forbidden to read from a such variable.

Is the above function intended to be conforming?

ANSWER:

The example was not intended to be conforming.
An edit is provided to correct this oversight.

EDIT to 24-007:

[348:7+] 15.8 Simple procedures, immediately after the antepenultimate
         constraint C15115 "A simple subprogram shall...",
         insert new constraint
 "C15115a A simple subprogram shall not contain an <image-selector>."

{Or, "...not contain the designator of a coindexed object",
 but <image-selector> seems simpler.}

SUBMITTED BY: Malcolm Cohen

HISTORY: 26-nnn   m241  Submitted

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