    {-# LANGUAGE Rank2Types #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Data.Typeable.Lens
    -- Copyright   :  (C) 2012-16 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 Prelude ()

    import Control.Lens
    import Control.Lens.Internal.Prelude
    import Data.Maybe (fromMaybe)
    import Data.Typeable

    -- | A 'Traversal'' for working with a 'cast' of a 'Typeable' value.
    _cast :: (Typeable s, Typeable a) => Traversal' s a
    _cast :: forall s a. (Typeable s, Typeable a) => Traversal' s a
    _cast a -> f a
    f s
    s = case s -> Maybe a
    forall a b. (Typeable a, Typeable b) => a -> Maybe b
    cast s
    s of
      Just a
    a  -> s -> Maybe s -> s
    forall a. a -> Maybe a -> a
    fromMaybe ([Char] -> s
    forall a. HasCallStack => [Char] -> a
    error [Char]
    "_cast: recast failed") (Maybe s -> s) -> (a -> Maybe s) -> a -> s
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . a -> Maybe s
    forall a b. (Typeable a, Typeable b) => a -> Maybe b
    cast (a -> s) -> f a -> f s
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> a -> f a
    f a
    a
      Maybe a
    Nothing -> s -> f s
    forall a. a -> f a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure s
    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 :: forall s a (c :: * -> *).
    (Typeable s, Typeable a) =>
    Traversal' (c s) (c a)
    _gcast c a -> f (c a)
    f c s
    s = case c s -> Maybe (c a)
    forall {k} (a :: k) (b :: k) (c :: k -> *).
    (Typeable a, Typeable b) =>
    c a -> Maybe (c b)
    gcast c s
    s of
      Just c a
    a  -> c s -> Maybe (c s) -> c s
    forall a. a -> Maybe a -> a
    fromMaybe ([Char] -> c s
    forall a. HasCallStack => [Char] -> a
    error [Char]
    "_gcast: recast failed") (Maybe (c s) -> c s) -> (c a -> Maybe (c s)) -> c a -> c s
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . c a -> Maybe (c s)
    forall {k} (a :: k) (b :: k) (c :: k -> *).
    (Typeable a, Typeable b) =>
    c a -> Maybe (c b)
    gcast (c a -> c s) -> f (c a) -> f (c s)
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> c a -> f (c a)
    f c a
    a
      Maybe (c a)
    Nothing -> c s -> f (c s)
    forall a. a -> f a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure c s
    s
    {-# INLINE _gcast #-}