GHC 8 and Template Haskell

Austin Seipp austin at
Thu Apr 14 18:17:46 UTC 2016

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

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

On Thu, Apr 14, 2016 at 1:12 PM, Ben Gamari <ben at> wrote:
> Iavor Diatchki <iavor.diatchki at> 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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Austin Seipp, Haskell Consultant
Well-Typed LLP,

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