DynamicLens.hs

import Control.Lens
import Data.Typeable
import Data.Dynamic

dynamicLens :: Typeable a => (Lens' s a) -> Lens' s Dynamic
dynamicLens l = lens getter setter
  where
    getter s = toDyn $ view l s
    setter s b =
        case fromDynamic b of
            Nothing -> s
            Just b' -> set l b' s

dynamicTraversal :: Typeable a => (Lens' s a) -> LensLike' Maybe s Dynamic
dynamicTraversal l f s = do
    let a = view l s
    altered <- f (toDyn a)
    casted <- fromDynamic altered
    return $ set l casted s