[Haskell-cafe] Help with TH trick

[David Feuer]

I must admit that looks rather mysterious to me. The documentation I saw
doesn't make the benefit of the nested splice terribly obvious.

On Tue, Oct 25, 2022, 10:53 PM Michael Sloan <mgsloan at gmail.com> wrote:

> You might also be interested in
> https://hackage.haskell.org/package/th-utilities-0.2.5.0/docs/TH-Derive.html -
> though afaik it didn't catch on.
>
> The cleverness there is to use nesting splicing, where the inner one
> generates code involving something like "runDeriver (Proxy @ Storable X)
> ...", where runDeriver is a method of a typeclass.  The instances of this
> class implement the code generation that is ultimately used for the output.
>
> $($(derive [d|
>         instance Deriving (Storable X)
>         |]))
>
>
> On Sat, Oct 22, 2022, 13:48 David Feuer <david.feuer at gmail.com> wrote:
>
>> Okay, I found it: recursion-schemes.
>>
>> On Sat, Oct 22, 2022, 3:05 PM David Feuer <david.feuer at gmail.com> wrote:
>>
>>> That doesn't work out so well when the class has a bunch of methods. I
>>> definitely saw the nice way on Hackage ... somewhere.
>>>
>>> On Sat, Oct 22, 2022, 2:49 PM Brandon Allbery <allbery.b at gmail.com>
>>> wrote:
>>>
>>>> I'm not aware of anything specifically like that, but the `make…`
>>>> functions in
>>>> https://hackage.haskell.org/package/deriving-compat-0.6.1/docs/Data-Deriving.html
>>>> may allow you to do something similar?
>>>>
>>>> On Sat, Oct 22, 2022 at 2:32 PM David Feuer <david.feuer at gmail.com>
>>>> wrote:
>>>> >
>>>> > I remember seeing a package that offered a function used something
>>>> like this:
>>>> >
>>>> > $(deriveThingy [d| instance Foo a => Thingy a |])
>>>> >
>>>> > to allow the user to specify the constraint(s) for a generated
>>>> instance. I'd love to borrow the code for that, but I can't remember what
>>>> package it was in, what class it derived, etc. Can anyone help?
>>>> > _______________________________________________
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>>>>
>>>>
>>>>
>>>> --
>>>> brandon s allbery kf8nh
>>>> allbery.b at gmail.com
>>>>
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