Re: [Haskell-cafe] Help with TH trick

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 wrote:

Okay, I found it: recursion-schemes.

On Sat, Oct 22, 2022, 3:05 PM David Feuer 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 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... may allow you to do something similar?

On Sat, Oct 22, 2022 at 2:32 PM David Feuer 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@gmail.com

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