To: J3                                                     J3/21-170r1
From:    Van Snyder & JOR
Subject: 16.10.2.24 OUTPUT_UNIT needs to specify it works for PRINT
Date: 2021-October-19
Reference: 21-007, 21-170

This r1 paper has updated line and subclause numbers for edits
(21-007r2 instead of F18), and additional explanatory comments.

1. Introduction
---------------

(new commentary)
Subclause 12.6.4.3 [247:7-16] discusses all the UNIT stuff for READs
without an io-control-list, the * for READ and WRITE, and PRINT unit
stuff.  But that subclause is far removed from 12.5.1, where SOME of
the unit stuff is discussed. This paper makes those two subclauses more
consistent.  16.10.2.13 also discusses INPUT_UNIT, and 16.10.2.24
discusses OUTPUT_UNIT, but neglects to mention the PRINT statement.
(end new commentary)

Subclause 12.5.1p4 "Referring to a file" specifies that the unit used in
a READ statement that does not specify a unit is the same as the unit
used in a READ statement in which the unit is specified by an asterisk,
and that this is the same unit as defined by the INPUT_UNIT named
constant in the intrinsic module ISO_FORTRAN_ENV.

That paragraph goes on to specify that the unit used in a WRITE
statement in which the unit is specified by an asterisk is the same unit
as defined by the OUTPUT_UNIT named constant in the intrinsic module
ISO_FORTRAN_ENV, but does not mention the PRINT statement.

Subclause 16.10.2.13 "INPUT_UNIT" specifies that the unit specified by
an asterisk is the same as the unit defined by INPUT_UNIT and the same
as the unit used in a READ statement that does not include an
input/output control list. This needs to be specified in 12.4.1p4.

That the asterisk unit in a WRITE statement might be believed to be the
same unit as the one used in a PRINT statement is suggested in subclause
12.6.4.8.3p4 "Executing defined input/output data transfers" in the
second list item:

     If the parent data transfer statement is a WRITE statement with an
     asterisk unit or a PRINT statement, the unit argument shall have
     the same value as the named constant OUTPUT_UNIT in the intrinsic
     module ISO_FORTRAN_ENV.

This needs to be made explicit in 12.5.1p4, and in 16.10.2.24
"OUTPUT_UNIT".  (new commentary) Also see 12.6.4.3. (end new commentary)

2. Edits
--------

[230:15] After "(16.10.2.13)." add
    "This unit is also used by a READ statement
     without an io-control-spec-list."

[230:17] After "ISO_FORTRAN_ENV (16.10.2.24)" add
     "This unit is also used by the PRINT statement."

[457:14] After "(12.6.4.3)" insert

     "; this unit is the one used by a PRINT statement"