Seamless combination of RVs and Rules with ReaderT r IO

[ivanperez-keera]

The following construction is very common:

installRule cenv = do
  f <- someFieldOfAnUIElement <$> someUIElement (uiBuilder (view cenv))
  let f2 - someFieldOfTheModel (model cenv))

 f =:= f2

The cenv is being passed around. Ideally, we'd want to write:

installRule =
  (someFieldOfAnUIElement . someUIElement) =:= someFieldOfTheModel

An initial approximation would be possible if we make RVs and RRs run on a reader monad with cenv in the environment. Some additional modifications would be necessary to make model and uiBuilder.view somehow implicit, and to make the (<$>) go away.