{-# LANGUAGE CPP #-} {-# LANGUAGE Rank2Types #-} #ifdef TRUSTWORTHY {-# LANGUAGE Trustworthy #-} #endif ----------------------------------------------------------------------------- -- | -- Module : Data.Typeable.Lens -- Copyright : (C) 2012-14 Edward Kmett -- License : BSD-style (see the file LICENSE) -- Maintainer : Edward Kmett <ekmett@gmail.com> -- Stability : experimental -- Portability : Rank2Types -- ---------------------------------------------------------------------------- module Data.Typeable.Lens ( _cast , _gcast ) where import Control.Applicative import Control.Lens import Data.Typeable import Data.Maybe -- | A 'Traversal'' for working with a 'cast' of a 'Typeable' value. _cast :: (Typeable s, Typeable a) => Traversal' s a _cast f s = case cast s of Just a -> fromMaybe (error "_cast: recast failed") . cast <$> f a Nothing -> pure s {-# INLINE _cast #-} -- | A 'Traversal'' for working with a 'gcast' of a 'Typeable' value. _gcast :: (Typeable s, Typeable a) => Traversal' (c s) (c a) _gcast f s = case gcast s of Just a -> fromMaybe (error "_gcast: recast failed") . gcast <$> f a Nothing -> pure s {-# INLINE _gcast #-}