content: {-# LANGUAGE Rank2Types #-}
  -----------------------------------------------------------------------------
  -- |
  -- Module      :  Data.HashSet.Lens
  -- Copyright   :  (C) 2012-16 Edward Kmett
  -- License     :  BSD-style (see the file LICENSE)
  -- Maintainer  :  Edward Kmett <ekmett@gmail.com>
  -- Stability   :  provisional
  -- Portability :  portable
  --
  ----------------------------------------------------------------------------
  module Data.HashSet.Lens
    ( setmapped
    , setOf
    , hashMap
    ) where
  
  import Control.Lens.Getter (Getting, views)
  import Control.Lens.Iso (iso)
  import Control.Lens.Setter (setting)
  import Control.Lens.Type
  import qualified Data.HashSet as HashSet
  import Data.HashSet (HashSet, fromMap, toMap)
  import Data.HashMap.Lazy (HashMap)
  import Data.Hashable
  
  -- $setup
  -- >>> :set -XNoOverloadedStrings
  -- >>> import Control.Lens
  
  -- | This 'Setter' can be used to change the type of a 'HashSet' by mapping
  -- the elements to new values.
  --
  -- Sadly, you can't create a valid 'Traversal' for a 'Set', but you can
  -- manipulate it by reading using 'Control.Lens.Fold.folded' and reindexing it via 'setmapped'.
  setmapped :: (Eq j, Hashable j) => IndexPreservingSetter (HashSet i) (HashSet j) i j
  setmapped = setting HashSet.map
  {-# INLINE setmapped #-}
  
  -- | Construct a set from a 'Getter', 'Control.Lens.Fold.Fold', 'Control.Lens.Traversal.Traversal', 'Control.Lens.Lens.Lens' or 'Control.Lens.Iso.Iso'.
  --
  -- @
  -- 'setOf' :: 'Hashable' a         => 'Getter' s a     -> s -> 'HashSet' a
  -- 'setOf' :: ('Eq' a, 'Hashable' a) => 'Fold' s a       -> s -> 'HashSet' a
  -- 'setOf' :: 'Hashable' a         => 'Iso'' s a       -> s -> 'HashSet' a
  -- 'setOf' :: 'Hashable' a         => 'Lens'' s a      -> s -> 'HashSet' a
  -- 'setOf' :: ('Eq' a, 'Hashable' a) => 'Traversal'' s a -> s -> 'HashSet' a
  -- @
  setOf :: Hashable a => Getting (HashSet a) s a -> s -> HashSet a
  setOf l = views l HashSet.singleton
  {-# INLINE setOf #-}
  
  -- | An `Iso` between a `HashSet` and a `HashMap` with unit values. \(\mathcal{O}(1)\).
  hashMap :: Iso' (HashSet a) (HashMap a ())
  hashMap = iso toMap fromMap
  