[J3] Consideration of Paper 18-242 at Meeting 218 (Was: 18-242)

[Bill Long]

> On Dec 1, 2018, at 2:29 PM, Van Snyder via J3 <j3 at mailman.j3-fortran.org> wrote:
> 
> 
> A loop-control declared in the statement would be a construct entity.
> That's the point!  It's not an accidental defect.

But the do-variable in an ordinary DO look is NOT a construct entity. The DO semantics depend on this.   I was not part of the JoR discussion, but it seems you are really proposing a whole new, separate form of DO.   For example:

integer(4) :: i

do integer(8) :: i = n,m
   if (a(i) < 0) exit
end do

call histo(i)  ! Corresponding dummy variable to i  is integer(4)

If the integer(8) :: is removed, then this is an ordinary loop.  If the 3rd iteration exits, the argument to histo has the value n+2 (assuming m > n+2), and has kind 4, which is what histo is expecting.  With the integer(8)::, if I understand your email description, the value if i is undefined at the call to histo.    If you really want this behavior, then write

block
integer(8) :: i
do i = n,m
  if (a(i) < 0) exit
end do
end block

At the end block, it is at least obvious to the programmer that the i declared in the block cannot be used.  At least this version does not violate the principle of least surprise. 

I think I have to agree with the JoR decision.  The benefit vs confusion balance favors not adding this feature. 

Cheers,
Bill



Bill Long                                                                       longb at cray.com
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