[J3] Why is += missing?

[Milan Curcic]

Thanks, Jeff.

I use this in other languages and miss it in Fortran, especially for more
verbose increments. I'd welcome it and support the proposal for F202Y.
Let's work on it.

Milan

On Thu, Aug 26, 2021 at 8:05 AM Jeff Hammond via J3 <
j3 at mailman.j3-fortran.org> wrote:

> RB:
>
>
>
> I agree with this idea.  I was thinking adding a “.” to make it like
> element-wise ops in Matlab might be acceptable. I am willing to add pretty
> much any character or character pair in order to avoid duplicating array
> expressions.
>
>
>
> MK:
>
>
>
> What happens to “a += b * c” is often optimized to an FMA if the compiler
> flags or defaults allow ISO/IEEE violation.  You have to talk nicely to GCC
> to get it to do it, whereas ICC will do it at -O1 and above.
>
>
>
> KH:
>
>
>
> Yeah, ÷ is available on my Mac but I assume it’s Unicode.  I am not
> advocating for the use of special characters in Fortran, but I wanted to
> use it in this thread so as to not overload /= even if it’s mostly obvious
> what I mean.
>
>
>
> Jeff
>
>
>
> *From: *J3 <j3-bounces at mailman.j3-fortran.org> on behalf of Bader,
> Reinhold via J3 <j3 at mailman.j3-fortran.org>
> *Date: *Wednesday, August 25, 2021 at 5:29 PM
> *To: *General J3 interest list <j3 at mailman.j3-fortran.org>
> *Cc: *Bader, Reinhold <Reinhold.Bader at lrz.de>
> *Subject: *Re: [J3] Why is += missing?
>
> *External email: Use caution opening links or attachments*
>
>
>
> Dear all,
>
>
>
> I think a separate syntax should be considered for these operations if
> they are accepted as an addition to the language. e.g.  +.=, -.= etc.
>
> Wrt /= it is not only the semantic overlap that is an issue but also the
> cognitive load on the programmer (prospective newby: “why the damn has /= a
> different meaning than +=?”)
>
>
>
> Also note that for a significant subset use of the associate construct
> allows to often write
>
>
>
> ASSOCIATE(X => something complicated)
>
> ...
>
>    X = X + Y
>
> END ASSOCIATE
>
>
>
> Regards
>
> Reinhold
>
>
>
> *Von:* J3 <j3-bounces at mailman.j3-fortran.org> *Im Auftrag von *Carlson,
> Neil via J3
> *Gesendet:* Mittwoch, 25. August 2021 16:03
> *An:* General J3 interest list <j3 at mailman.j3-fortran.org>
> *Cc:* Carlson, Neil <nnc at lanl.gov>
> *Betreff:* Re: [J3] Why is += missing?
>
>
>
> Jeff's point here is spot on.  The point of "+=" isn't simply about
> convenience.  It expresses intent.  A primary purposes of a high level
> language is to support code that can be more easily understood and reasoned
> about (by a human).  If your example is "a = a + 1" then sure "+=" looks
> like insignificant syntactic sugar.  But in his original example one has to
> carefully look at both sides of the "=" to understand that the intent is to
> increment.  The desire to have a complete set of such operators is
> obviously understandable.  But it's not right that a difficulty posed by
> "/=" should derail them all ("perfect is the enemy of good") -- having just
> "+=" and "-=" would be a major improvement to the language.
>
>
>
> Neil
>
>
> ------------------------------
>
> *From:* J3 <j3-bounces at mailman.j3-fortran.org> on behalf of Jeff Hammond
> via J3 <j3 at mailman.j3-fortran.org>
> *Sent:* Wednesday, August 25, 2021 7:27 AM
> *To:* General J3 interest list
> *Cc:* Jeff Hammond
> *Subject:* [EXTERNAL] Re: [J3] Why is += missing?
>
>
>
> I will argue that it is syntactic sugar in the same sense that
> multidimensional arrays are.  Below is the perfectly functional C code I
> wrote to match my Fortran years ago (because computer scientists don’t know
> their history).  There is no actual need for multidimensional arrays in
> Fortran, just the practical difficulty of not having them.
>
>
>
> // t3(h3,h2,h1,p6,p5,p4)+=t1(p4,h1)*v2(h3,h2,p6,p5);
>
> t3[h3+h3u*(h2+h2u*(h1+h1u*(p6+p6u*(p5+p5u*p4))))] += t1[p4+p4u*h1] *
> v2[h3+h3u*(h2+h2u*(p6+p6u*p5))];
>
>
>
> I think the relative usage of +=, -=, *=, ÷=, and **= if they were added
> justifies the pragmatic solution of just doing += and -=, which are more
> likely to have hardware support anyways.
>
>
>
> Jeff
>
>
>
> *From: *J3 <j3-bounces at mailman.j3-fortran.org> on behalf of Steve Lionel
> via J3 <j3 at mailman.j3-fortran.org>
> *Date: *Wednesday, August 25, 2021 at 4:13 PM
> *To: *j3 at mailman.j3-fortran.org <j3 at mailman.j3-fortran.org>
> *Cc: *Steve Lionel <steve at stevelionel.com>
> *Subject: *Re: [J3] Why is += missing?
>
> *External email: Use caution opening links or attachments*
>
>
>
> On 8/25/2021 8:07 AM, Jeff Hammond via J3 wrote:
>
> After 15 years as a Fortran programmer, I am still annoyed on a daily
> basis about the tedium imposed on me because Fortran lacks +=.
>
> This was considered - there were a few requests for it in the 202X survey
> we ran 2017-2018. I suspect it fell off the list because of 1)  it is
> "syntactic sugar", not adding any new capability and 2) the existing use of
> /= requiring some complicated exceptions. It could be done, sure, but the
> demand seems low. We'll soon start the process for 202Y features - feel
> free to put it forward then.
>
>
>
> Steve
>
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