module Agda.Utils.Lens
( module Agda.Utils.Lens
, (<&>)
) where
import Control.Applicative ( Const(Const), getConst )
import Control.Monad.State
import Control.Monad.Reader
import Control.Monad.Writer
import Data.Map (Map)
import qualified Data.Map as Map
import Data.Functor.Identity
import Agda.Utils.Functor ((<&>))
type Lens' i o = forall f. Functor f => (i -> f i) -> o -> f o
infixl 8 ^.
(^.) :: o -> Lens' i o -> i
o ^. l = getConst $ l Const o
set :: Lens' i o -> i -> o -> o
set l = over l . const
over :: Lens' i o -> (i -> i) -> o -> o
over l f o = runIdentity $ l (Identity . f) o
use :: MonadState o m => Lens' i o -> m i
use l = do !x <- gets (^. l)
return x
infix 4 .=
(.=) :: MonadState o m => Lens' i o -> i -> m ()
l .= i = modify $ set l i
infix 4 %=
(%=) :: MonadState o m => Lens' i o -> (i -> i) -> m ()
l %= f = modify $ over l f
infix 4 %==
(%==)
#if __GLASGOW_HASKELL__ <= 708
:: (Functor m, MonadState o m)
#else
:: MonadState o m
#endif
=> Lens' i o -> (i -> m i) -> m ()
l %== f = put =<< l f =<< get
infix 4 %%=
(%%=)
#if __GLASGOW_HASKELL__ <= 708
:: (Functor m, MonadState o m)
#else
:: MonadState o m
#endif
=> Lens' i o -> (i -> m (i, r)) -> m r
l %%= f = do
o <- get
(o', r) <- runWriterT $ l (WriterT . f) o
put o'
return r
view :: MonadReader o m => Lens' i o -> m i
view l = asks (^. l)
locally :: MonadReader o m => Lens' i o -> (i -> i) -> m a -> m a
locally l = local . over l
key :: Ord k => k -> Lens' (Maybe v) (Map k v)
key k f m = f (Map.lookup k m) <&> \ v -> Map.alter (const v) k m