08-201
To: J3
From: Van Snyder
Subject: Construct-scope DO variable
Date: 2008 May 31
References: 08-007r2

1.  Introduction

To avoid requiring the wordy circumlocution

  DO BLOCK
    INTEGER :: I
    DO I = 1, 10
    ...
    END DO
  END BLOCK

just to get a construct-scope <do-variable>, do the same for a
<do-construct> that we have done for the FORALL and DO CONCURRENT
constructs, viz., allow <type-spec> :: before the <do-variable> -- but
only in a <block-do-construct>:

  DO INTEGER :: I = 1, 10
    ...
  END DO

This would reduce the number of "Why not?" surprises that students of
Fortran must endure.

There are two possibilities: Allow the <type-spec> only in a
<nonlabel-do-stmt>, and allow it in any <block-do-construct>.  The
latter might be more difficult for processors.  It cannot be allowed in
nonblock DO constructs because the scopes would overlap:  Which I should
be used in the shared do-term statement?

  DO 1 INTEGER :: I = 1, 2
    DO 1 INTEGER :: I = 3, 4
1 PRINT *, I

2.  Edits for only on a <nonlabel-do-stmt>

[176: 8.1.7.2 R827] ----------------------------------------------------
Editor: Insert "[ <type-spec> :: ]" before "<scalar-int-variable-name>".

[176: 8.1.7.2 C816] ----------------------------------------------------
Editor: Replace C816:

"C816  (R827) The <type-spec> shall specify integer type.

"C816a (R827) A <type-spec> shall not appear in a <label-do-stmt>.

"C816b (R827) If <type-spec> does not appear, <do-variable> shall be a
       variable of integer type."

[176: C819+] -----------------------------------------------------------
Editor: Insert a note:

"NOTE 8.10a
A <type-spec> is not permitted in a <label-do-stmt> because the ranges
of nested nonblock DO constructs overlap, and therefore the scopes of
construct-scope DO variables would overlap."

[177: 8.1.7.4p1+ or 8.1.7.4p2+] ----------------------------------------
Editor: Insert a new paragraph:

"If <type-spec> appears, the <do-variable> in a <block-do-construct> has
a scope of the construct (16.4).  It is a scalar variable that has the
specified type and type parameters; it has no other attributes."

[442: 16.4p1] ----------------------------------------------------------
Editor: Insert a sentence at the end of the paragraph:

"A variable that appears as the <do-variable> in a <do-stmt> in which a
<type-spec> appears is a construct entity."

3.  Edits for only in a <block-do-construct>

[176: 8.1.7.2 R827] ----------------------------------------------------
Editor: Insert "[ <type-spec> :: ]" before "<scalar-int-variable-name>".

[176: 8.1.7.2 C816] ----------------------------------------------------
Editor: Replace C816:

"C816  (R827) The <type-spec> shall specify integer type.

"C816a (R827) If <type-spec> does not appear, <do-variable> shall be a
       variable of integer type."

[176: R834+] -----------------------------------------------------------
Editor: Insert a constraint:

"C819a (R831) A <type-spec> shall not appear in a <label-do-stmt> in a
       <nonblock-do-construct>."

[177: C823+ or 8.1.7.3p2+] ---------------------------------------------
Editor: Insert a note:

"NOTE 8.10a
A <type-spec> is not permitted in a <nonblock-do-construct> because the
ranges of nested nonblock DO constructs overlap, and therefore the
scopes of construct-scope DO variables would overlap."

[177: 8.1.7.4p1+ or 8.1.7.4p2+] ----------------------------------------
Editor: Insert a new paragraph:

"If <type-spec> appears, the <do-variable> in a <block-do-construct> has
a scope of the construct (16.4).  It is a scalar variable that has the
specified type and type parameters; it has no other attributes."

[442: 16.4p1] ----------------------------------------------------------
Editor: Insert a sentence at the end of the paragraph:

"A variable that appears as the <do-variable> in a <do-stmt> in which a
<type-spec> appears is a construct entity."