T16946.hs:11:9: error: [GHC-71451]
    • Cannot generalise type; skolem ‘k’ would escape its scope
      if I tried to quantify (y0 :: k) in this type:
        forall k (c :: k -> k -> *)
               (m :: forall (x :: k) (y :: k). c x y -> * -> *) a.
        CatMonad @k c m =>
        a -> m @y0 @y0 (Id @{k} @y0 c) a
      (Indeed, I sometimes struggle even printing this correctly,
       due to its ill-scoped nature.)
    • In the type signature:
        boom :: forall k
                       (c :: k -> k -> Type)
                       (m :: forall (x :: k) (y :: k). c x y -> Type -> Type)
                       a.
                CatMonad c m => a -> m (Id c) a