如何使用單例庫為存在量化類型定義HasRep實例？

Question

我想使用存在大小的圖像窗口有幾個原因：

• 我想將不同大小的窗口打包到同一個列表中。
• 我想為我的窗口類型創建一個Zip實例。

我正在使用此代碼執行此操作：

-- | A "matrix" represented as a composition of sized vectors.
type Mat h w = Vector h :.: Vector w

-- | A handy alias for locating a window in the 2D plane.
type Orig = (Integer,Integer)

-- | An attempt at using `singletons` to define windows.
data Wind :: Nat -> Nat -> Type -> Type where  -- height -> width
  Wind
    :: (KnownNat h, KnownNat w)
    => { img  :: Mat h w a  -- ^ image data matrix
       , ll   :: Orig       -- ^ position of lower-left corner
       , dflt :: a          -- ^ out-of-bounds value
       } -> Wind h w a

data SomeWind a :: Type where
  MkSomeWind :: Sing h -> Sing w -> Wind h w a -> SomeWind a

現在，我需要為SomeWind類型創建一個HasRep實例：

import qualified ConCat.Rep as R

instance R.HasRep (SomeWind a) where
  type Rep (SomeWind a) = ???
  repr (MkSomeWind _ _ (Wind im orig def)) = (im, (orig, def))
  abst (im :: (Vector h :.: Vector w) a, (orig, def)) =
    MkSomeWind (SNat :: Sing h) (SNat :: Sing w) (Wind im orig def)

我有一種嘮叨的預感，我應該能夠使用單身人士庫來幫助我取代“???” 上面有正確的定義，但我無法弄清楚如何。

有人可以幫忙嗎？