What is relation between PickFn, LayoutPick and Renderable?

[cblp]

They are incompatible, and it makes it hard to combine grids of different layouts (see #217).

I'm trying to make them compatible. I have two hypotheses:

1. If LayoutPick and PickFn are on the same level of abstraction, then why they are not compatible? I don't see an easy way to convert between a function and a structure.

2. If they are entities of different "kinds", then LayoutPick may be wrapped in PickFn with const . Just, but I don't think this is a proper way, because this leads to PickFn (PickFn (LayoutPick _)) in rendering functions.

When I use functions like this:

renderableToFile def "/tmp/a.png"
  :: Renderable a -> IO (PickFn a)

renderableToFile def "/tmp/a.png" $ gridToRenderable $ layoutToGrid def
  :: (PlotValue x, PlotValue y) =>
     IO (PickFn (LayoutPick x y y))

it looks like they are on different levels, and Renderable expects the argument to be LayoutPick to wrap it then in PickFn.

But when I use

pieChartToRenderable :: forall a. PieChart -> Renderable (PickFn a)

it happens that Renderable expects its argument to be PickFn! To wrap it into what?

renderableToFile def "/tmp/a.png" $ pieChartToRenderable def
  :: IO (PickFn (PickFn a))

Double PickFn?