To: J3                                                     J3/20-153
From: Robert Corbett
Subject: ambiguous READ
References: 20-007
Date: 2020-October-12

The statement

      READ (CVAR)

where CVAR is a default character variable is syntactically
ambiguous.  Under the syntax rules, it might be a input
statement that designates an internal file, or it might be
a formatted input statement that reads from the default
input unit.

If the statement is interpreted as an input statement that
reads from an internal file, it is not standard conformant.
Paragraph 2 of subclause 12.6.4.3 "Identifying a unit" of
20-007 states

    The unit identified by an unformatted data transfer
    statement shall be an external unit.

The interpretation of the statement as a formatted input
statement has no such problem.

For the sake of resolving the syntactic ambiguity, the
restriction given in subclause 12.6.4.3 should be promoted
to a constraint.  Edits to that effect are supplied.

EDITS to 20-007:
[12.6.1 "Form of input and output statements" p1+,
 page:9-]
Following Note 1, insert the new note
 "Note 2
  A statement of the form

      READ (\su{name})

  where \su{name} is the name of a default character
  variable is a formatted input statement.  It cannot be an
  input statement that specifies an internal file because
  of C1219a."

[12.6.2.1 "Syntax" p1+, page 233:13+]
Insert
 "C1219a (R1213)  If \si{io-unit} is an
         \si{internal-file-variable}, the
         \si{io-control-spec-list} shall contain a
         \s1{format} or a \si{namelist-group-name}.