GHC 8 and Template Haskell

[Eric Seidel]

I think a general "no TH changes after the first RC" seems reasonable as
part of the broader feature freeze. 

But this case seems decidedly more of a bug fix than a feature addition,
since TH *should* have feature parity with Haskell syntax. So I'd favor
merging Iavor's patch.

I also like Austin's suggestion that we require template-haskell patches
alongside new syntax.

Eric

On Thu, Apr 14, 2016, at 13:59, Richard Eisenberg wrote:
> I'm happy to be overruled on this, but I vote against this change for GHC
> 8. Personally, I like to have a policy of "no TH changes after the first
> RC". This gives ample time for TH clients to update their code. Iavor's
> suggestion would likely involve a new part of the InstanceD constructor,
> which would affect anyone constructing or matching on this constructor.
> If the change involved, say, only adding new functionality without
> changing anything existing, I would be more willing to include for GHC 8.
> 
> And, yes, I agree with Austin.
> 
> Richard
> 
> On Apr 14, 2016, at 2:17 PM, Austin Seipp <austin at well-typed.com> wrote:
> 
> > Here's a question, on top of this one: why don't we require
> > template-haskell changes for most corresponding syntax changes? We
> > tend to play catch up with template-haskell sometimes and it's
> > relatively strange. I mean, in some sense, we could have said a while
> > back "This needs another revision, please add template haskell
> > support" and avoided it all.
> > 
> > Richard has a better insight into this than I do, I'm sure, but it
> > seems - to me, anyway - like template-haskell support is a reasonable
> > bar for most surface-level syntax change to cross, before getting
> > merged.
> > 
> > My intuition tells me that, most of the time, a lot of us simply
> > forget to make the changes, or ask for them in reviews, and so it
> > goes.
> > 
> > On Thu, Apr 14, 2016 at 1:12 PM, Ben Gamari <ben at well-typed.com> wrote:
> >> Iavor Diatchki <iavor.diatchki at gmail.com> writes:
> >> 
> >>> Hello,
> >>> 
> >>> Now that "OVERLAPPING" and "OVERLAPPABLE" are pragmas on the instances, do
> >>> we have a way to generate instances with such pragmas using Template
> >>> Haskell?   I can't seem to find a way to do this, which is unfortunate.
> >>> 
> >>> If I am not missing anything, would there be objections to adding it to the
> >>> TH library before the next release---I would volunteer to do the change
> >>> ASAP.
> >>> 
> >> Indeed this is an unfortunate gap. Given that this shouldn't be a
> >> terribly invasive change I would be alright with this if Richard approves.
> >> 
> >> Cheers,
> >> 
> >> - Ben
> >> 
> >> 
> >> _______________________________________________
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> >> 
> > 
> > 
> > 
> > -- 
> > Regards,
> > 
> > Austin Seipp, Haskell Consultant
> > Well-Typed LLP, http://www.well-typed.com/
> 
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