I’m lost. Could you give me a bit more context?

I’m deeply suspicious about that ForallXImplicitBndrs thing with strange higher kinded parameters.   Smells all wrong to me.

Simon

From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Alan & Kim Zimmerman
Sent: 23 October 2017 16:07
To: ghc-devs@haskell.org
Subject: forall in constraint

I am working on the Trees that Grow stuff, and hit a small problem

I have

type family XIB               x thing
type family XNewImplicitBndrs x thing

type ForallXImplicitBndrs (c :: * -> Constraint) (x :: *) (thing :: *) =
       ( c (XIB               x thing)
       , c (XNewImplicitBndrs x thing)
       )

and I want to extend the DataId constraint

type DataId p =
  ( Data p

  , ForallXImplicitBndrs Data p thing
  )

But the problem is I do not have `thing` at this point, and to get it in the code will involve some hs-boot nastiness.

Is there any way to require "forall thing. Data thing" inside the DataId constraint?

Alan