[J3] Why is += missing?

[Bader, Reinhold]

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<mailto:j3-bounces at mailman.j3-fortran.org>> on behalf of Jeff Hammond via J3 <j3 at mailman.j3-fortran.org<mailto: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<mailto:j3-bounces at mailman.j3-fortran.org>> on behalf of Steve Lionel via J3 <j3 at mailman.j3-fortran.org<mailto:j3 at mailman.j3-fortran.org>>
Date: Wednesday, August 25, 2021 at 4:13 PM
To: j3 at mailman.j3-fortran.org<mailto:j3 at mailman.j3-fortran.org> <j3 at mailman.j3-fortran.org<mailto:j3 at mailman.j3-fortran.org>>
Cc: Steve Lionel <steve at stevelionel.com<mailto:steve at stevelionel.com>>
Subject: Re: [J3] Why is += missing?

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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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