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{-# LANGUAGE CPP #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE DeriveFoldable #-}
{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE DeriveTraversable #-}
{-# LANGUAGE KindSignatures #-}
module Data.Map.Util where
import Data.Data (Data, Typeable)
import Data.Map (Map)
import Data.Monoid -- so that the docs for Monoid link to the right place
import qualified Data.Map as M
#if !(MIN_VERSION_base(4,8,0))
import Data.Foldable (Foldable)
import Data.Traversable (Traversable)
#endif
-- | An internal index used to track ordering only -- its magnitude doesn't
-- matter. If you manage to see this documentation, the library author has made
-- a mistake!
type Tag = Int
-- | A 0-based index, much like the indices used by lists' '!!' operation. All
-- indices are with respect to insertion order.
type Index = Int
nextLowerTag, nextHigherTag :: Map Tag a -> Tag
nextLowerTag = maybe 0 pred . minTag
nextHigherTag = maybe 0 succ . maxTag
minTag, maxTag :: Map Tag a -> Maybe Tag
minTag m = fmap (fst . fst) (M.minViewWithKey m)
maxTag m = fmap (fst . fst) (M.maxViewWithKey m)
showsPrecList :: Show a => (b -> [a]) -> Int -> b -> ShowS
showsPrecList toList d o = showParen (d > 10) $
showString "fromList " . shows (toList o)
readsPrecList :: Read a => ([a] -> b) -> Int -> ReadS b
readsPrecList fromList d = readParen (d > 10) $ \r -> do
("fromList", s) <- lex r
(xs, t) <- reads s
return (fromList xs, t)
-- | A newtype to hang a 'Monoid' instance on. The phantom first parameter
-- tells whether 'mappend' will prefer the indices of its first or second
-- argument if there are shared elements in both.
--
-- @since 0.2
newtype Bias (dir :: IndexPreference) a = Bias { unbiased :: a }
deriving (Data, Eq, Foldable, Functor, Ord, Read, Show, Traversable, Typeable)
-- | @since 0.2
data IndexPreference = L | R
deriving Typeable
type L = 'L
type R = 'R
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