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{-# LANGUAGE CPP #-}
{-# LANGUAGE Rank2Types #-}
#ifdef TRUSTWORTHY
{-# LANGUAGE Trustworthy #-}
#endif
-----------------------------------------------------------------------------
-- |
-- Module : Data.Typeable.Lens
-- Copyright : (C) 2012 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 #-}
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