Template Haskell support for type families

[g9ks157k@…]

Would it be possible to add support for analyzing and generating type family stuff to Template Haskell?

[simonpj]

I don't think this is likely to happen any time soon.

TH has a data type for Haskell programs, completely separate from GHC's data type. This is a strength because it brings stablity, but a weakness because it means it always lags a long way behind.

In the case of type families, we barely have them working in GHC, so it'd might be a bit soon to dump them into TH. And even when they are stable there's the question of who will do the design and implementation. Perhaps some TH users can join in!

Meanwhile I'll put this as low priority.

Simon

[igloo]

I've put this in the 6.10 milestone for now, but it would probably need someone to jump in and implement it.

[hpacheco]

Myself, I would simply like to be able to write TH code to automatically generate type family instances. However, I understand it is not a very important feature.

[AndyGill]

Having this is important to the kure-your-boilerplate work. It would save quite a bit of typing for KURE users. Any chance for 6.12?

AndyG

[igloo]

Lots of interest, so I've raised the priority.

[chak]

I just pushed patches adding support for type family declarations (toplevel and associated) and equality constraints to TH.

The downside is that it changes the API of Language.Haskell.TH in an incompatible way (to distinguish between class constraints and equality constraints). Given that I had to change the API anyways, we agreed to add kinds, too. I'll do that in the next few days, but it'll change the API even a bit more.