Syntactic Sugar Idea for Go 2.0: until/unless, and postfix conditionals

[Jeffrey Paul]

Hello Gophers,

There's two tiny pieces of syntactic sugar I really miss from a few other languages that I think would add a nice bit of ergonomics and convenience to Go (which I now play as my main) without increasing any magic or spooky action at a distance.

They are:

- postfix conditionals

and

- until (while!) and unless (if!) (which probably also means adding `while`)

This allows for lovely expressions such as the following examples:

i.NotifySomeone() if j.HasExpiredItems()

time.Sleep(1 * time.Second) until thing.IsReady()

b.ReportActivity(e) unless u.HasOptedOut()

q.ProcessItem() while server.Active()

until(time.Now().After(notAfter)) {
// do something while we still can
}

p.processEvents() until p.shutdownRequested

and, my favorite:

panic("can't even") if err != nil

There are, of course, various ways of doing some of this sort of synchronization stuff in these contrived examples using channels/goroutines/timers, but this sort of syntax is quite useful for simple straight-line synchronous code, and, in my view, increases readability without sacrificing anything.

I know that `while` isn't a distinct thing in Go, and for consistency's sake, this might necessitate adding such a construct as well (if you can use it as a postfix conditional, you should probably be able to use it as `while(cond) {}` too).

What do you think? I really miss this syntax from other languages. It's been in Perl and Ruby for ages, and, more recently, CoffeeScript had it for a moment, but it didn't make it over into ES with the other notable features from it. I think it's a lovely convenience without changing the operation of the language itself.

Best,
-sneak

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[Dan Kortschak]

My first professional programming language was Perl, decades later I
still wake up in a sweat thinking about post-fix conditionals and the
'unless' conditional.

Please no.

[Tyler Compton]

I don't think I'm personally sold on this proposal either, but I'm curious what bad experiences you've had with post-fix conditionals. I haven't personally used a language with post-fix conditionals and it sounds like that might be to my benefit :)

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[Dan Kortschak]

There are two parts. The worse part is the negative conditional
(unless), which has the problem that humans are bad at negations;
nearly always when there is a complex condition with an "unless", it
needs to be mentally refactored into an "if !" (when working through
other people's bugs, I invariably — at least temporarily — inverted the
condition and replaced the "unless" with an "if").

The post-fix conditional syntax says a whole heap of stuff that's going
to happen, and only when you get to the end of the line do you see that
it might not.

Putting a single positively oriented syntax, at the front of
conditional blocks greatly simplifies the thinking about what is going
to happen in a section of code.

[Tyler Compton]

Thanks, Dan. Those seem like well-reasoned points.

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[Jan Mercl]

On Tue, Nov 3, 2020 at 6:09 AM 'Dan Kortschak' via golang-nuts
<golan...@googlegroups.com> wrote:

> My first professional programming language was Perl, decades later I
> still wake up in a sweat thinking about post-fix conditionals and the
> 'unless' conditional.

I don't miss MUMPS post conditional either.

[Marcin Romaszewicz]

Indeed!

Go has while loops :)

for {

  // do some stuff

  if !condition { break }

}

instead of

{

  // do some stuff

} while condition

They are identical functionally, so why bother with the second syntax? You then get into arguments about which one to use.

-- Marcin

On Tue, Nov 3, 2020 at 11:31 AM 'Amnon Cohen' via golang-nuts <golan...@googlegroups.com> wrote:

Languages often have a whole variety of loop constructs.
C has for loops as well us while loops.
Go adopts the principle from the Zen of python:
There should be one-- and preferably only one --obvious way to do it.
It takes a minimalist approach - there is only one looping construct: the for loop.

This is an excellent decision, IMO.

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