content: -----------------------------------------------------------------------------
  -- |
  -- Copyright   :  (C) 2014-2016 Edward Kmett
  -- License     :  BSD-style (see the file LICENSE)
  -- Maintainer  :  Edward Kmett <ekmett@gmail.com>
  -- Stability   :  experimental
  -- Portability :  non-portable
  --
  -- One of most commonly-asked questions about this package is whether
  -- it provides lenses for working with 'Data.Map.Map'. It does, but their uses
  -- are perhaps obscured by their genericity. This module exists to provide
  -- documentation for them.
  --
  -- 'Data.Map.Map' is an instance of 'Control.Lens.At.At', so we have a lenses
  -- on values at keys:
  --
  -- >>> Map.fromList [(1, "world")] ^.at 1
  -- Just "world"
  --
  -- >>> at 1 .~ Just "world" $ Map.empty
  -- fromList [(1,"world")]
  --
  -- >>> at 0 ?~ "hello" $ Map.empty
  -- fromList [(0,"hello")]
  --
  -- We can traverse, fold over, and map over key-value pairs in a
  -- 'Data.Map.Map', thanks to its 'Control.Lens.Indexed.TraversableWithIndex',
  -- 'Control.Lens.Indexed.FoldableWithIndex', and
  -- 'Control.Lens.Indexed.FunctorWithIndex' instances.
  --
  -- >>> imap const $ Map.fromList [(1, "Venus")]
  -- fromList [(1,1)]
  --
  -- >>> ifoldMap (\i _ -> Sum i) $ Map.fromList [(2, "Earth"), (3, "Mars")]
  -- Sum {getSum = 5}
  --
  -- >>> itraverse_ (curry print) $ Map.fromList [(4, "Jupiter")]
  -- (4,"Jupiter")
  --
  -- >>> itoList $ Map.fromList [(5, "Saturn")]
  -- [(5,"Saturn")]
  --
  -- A related class, 'Control.Lens.At.Ixed', allows us to use
  -- 'Control.Lens.At.ix' to traverse a value at a particular key.
  --
  -- >>> ix 2 %~ ("New " ++) $ Map.fromList [(2, "Earth")]
  -- fromList [(2,"New Earth")]
  --
  -- >>> preview (ix 8) $ Map.empty
  -- Nothing
  --
  -- Additionally, 'Data.Map.Map' has 'Control.Lens.Traversal.TraverseMin' and
  -- 'Control.Lens.Traversal.TraverseMax' instances, which let us traverse over
  -- the value at the least and greatest keys, respectively.
  --
  -- >>> preview traverseMin $ Map.fromList [(5, "Saturn"), (6, "Uranus")]
  -- Just "Saturn"
  --
  -- >>> preview traverseMax $ Map.fromList [(5, "Saturn"), (6, "Uranus")]
  -- Just "Uranus"
  --
  -----------------------------------------------------------------------------
  module Data.Map.Lens
    ( toMapOf
    ) where
  
  import Control.Lens.Getter ( IndexedGetting, iviews )
  import qualified Data.Map as Map
  
  -- $setup
  -- >>> import Control.Lens
  -- >>> import Data.Monoid
  -- >>> import qualified Data.Map as Map
  -- >>> :set -XNoOverloadedStrings
  
  -- | Construct a map from a 'IndexedGetter', 'Control.Lens.Fold.IndexedFold', 'Control.Lens.Traversal.IndexedTraversal' or 'Control.Lens.Lens.IndexedLens'
  --
  -- The construction is left-biased (see 'Data.Map.Lazy.union'), i.e. the first
  -- occurrences of keys in the fold or traversal order are preferred.
  --
  -- >>> toMapOf folded ["hello", "world"]
  -- fromList [(0,"hello"),(1,"world")]
  --
  -- >>> toMapOf (folded . ifolded) [('a',"alpha"),('b', "beta")]
  -- fromList [('a',"alpha"),('b',"beta")]
  --
  -- >>> toMapOf (folded <.> folded) ["foo", "bar"]
  -- fromList [((0,0),'f'),((0,1),'o'),((0,2),'o'),((1,0),'b'),((1,1),'a'),((1,2),'r')]
  --
  -- >>> toMapOf ifolded $ Map.fromList [('a', "hello"), ('b', "world")]
  -- fromList [('a',"hello"),('b',"world")]
  --
  -- @
  -- 'toMapOf' ::          'IndexedGetter' i s a     -> s -> 'Map.Map' i a
  -- 'toMapOf' :: 'Ord' i => 'IndexedFold' i s a       -> s -> 'Map.Map' i a
  -- 'toMapOf' ::          'IndexedLens'' i s a      -> s -> 'Map.Map' i a
  -- 'toMapOf' :: 'Ord' i => 'IndexedTraversal'' i s a -> s -> 'Map.Map' i a
  -- @
  toMapOf :: IndexedGetting i (Map.Map i a) s a -> s -> Map.Map i a
  toMapOf l = iviews l Map.singleton
  