Permitting trailing commas for record syntax ADT declarations

[Johan Tibell]

I must say that requiring a language pragma makes the feature quite a bit
more heavy weight. We're not changing the meaning of any existing programs,
just allowing some new ones. One could argue that perhaps the HaskellXX
standard might pick up this new pragma and thus making it unnecessary
eventually, but the standardization process is dead (and even when it was
alive, it was lagging actual practice enough that it was largely ignored.)


On Tue, Sep 23, 2014 at 9:41 AM, Roman Cheplyaka <roma at ro-che.info> wrote:

> On 23/09/14 10:11, Alexander Berntsen wrote:
> > On 22/09/14 21:07, Simon Peyton Jones wrote:
> >> have a language extension TrailingCommas (or something) to enable
> >> the extension
> > For clarification: are you overruling the "do we sneak it in HEAD or
> > use pragma(s)"-vote and telling me to do the latter?
> >
> > If we can sneak it into HEAD (this is @ you Johan, too), I suggest
> > that someone applies my patches to make import and export lists
> > support leading commas (presently they only support trailing commas,
> > per the report) -- and following this I can just send a bunch of
> > "Permit leading/trailing ',' in Foo" patches to Phabricator, and you
> > guys can bikeshed over there about which ones you actually want to
> > commit. ;-)
> >
> > If I am to go down the pragma route, I guess I can make a
> > RudundantCommas pragma or something like that, that implements
> > trailing commas for imports/exports, and leading/trailing commas for
> > the suggestions in this thread.
> >
> > I'm +1 on the GHC HEAD route, but I'm not exactly violently opposed to
> > the pragma route either.
>
> Here's my reasoning:
>
> If you invoke ghc with -XHaskell2010, then trailing commas shouldn't be
> accepted, because they do not belong to Haskell 2010.
>
> Which means that you do need an extension to identify this difference in
> behavior.
>
> Roman
>
>
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