{-# LANGUAGE CPP #-}
{-# LANGUAGE Rank2Types #-}
#ifndef MIN_VERSION_base
#define MIN_VERSION_base(x,y,z) 1
#endif
module Data.Typeable.Lens
( _cast
, _gcast
) where
import Control.Lens
import Data.Typeable
import Data.Maybe
#if !MIN_VERSION_base(4,8,0)
import Control.Applicative
#endif
_cast :: (Typeable s, Typeable a) => Traversal' s a
_cast :: Traversal' s a
_cast f :: a -> f a
f s :: s
s = case s -> Maybe a
forall a b. (Typeable a, Typeable b) => a -> Maybe b
cast s
s of
Just a :: a
a -> s -> Maybe s -> s
forall a. a -> Maybe a -> a
fromMaybe ([Char] -> s
forall a. HasCallStack => [Char] -> a
error "_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
<$> a -> f a
f a
a
Nothing -> s -> f s
forall (f :: * -> *) a. Applicative f => a -> f a
pure s
s
{-# INLINE _cast #-}
_gcast :: (Typeable s, Typeable a) => Traversal' (c s) (c a)
_gcast :: Traversal' (c s) (c a)
_gcast f :: c a -> f (c a)
f s :: c s
s = case c s -> Maybe (c a)
forall k (a :: k) (b :: k) (c :: k -> *).
(Typeable a, Typeable b) =>
c a -> Maybe (c b)
gcast c s
s of
Just a :: c a
a -> c s -> Maybe (c s) -> c s
forall a. a -> Maybe a -> a
fromMaybe ([Char] -> c s
forall a. HasCallStack => [Char] -> a
error "_gcast: recast failed") (Maybe (c s) -> c s) -> (c a -> Maybe (c s)) -> c a -> c s
forall b c a. (b -> c) -> (a -> b) -> a -> c
. c a -> Maybe (c s)
forall k (a :: k) (b :: k) (c :: k -> *).
(Typeable a, Typeable b) =>
c a -> Maybe (c b)
gcast (c a -> c s) -> f (c a) -> f (c s)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> c a -> f (c a)
f c a
a
Nothing -> c s -> f (c s)
forall (f :: * -> *) a. Applicative f => a -> f a
pure c s
s
{-# INLINE _gcast #-}