Cuckoo.hs

-- |
-- Module      :  Case.Hashable.Cuckoo
-- Copyright   :  (c) OleksandrZhabenko 2021
-- License     :  MIT
-- Stability   :  Experimental
-- Maintainer  :  olexandr543@yahoo.com
--
-- A library that can be used as a @case ... of@ constuction analogue for the Hashable keys.
-- For the large lists is expected to be more time efficient than CaseBi.Arr.getBFst' analogue.
-- If you plan to use it together with the former one, please, use qualified import to avoid names ambiguity.


{-# LANGUAGE MagicHash, UnboxedTuples #-}

module Case.Hashable.Cuckoo (
  getBFstL'
) where

import qualified Data.HashTable.ST.Cuckoo as C
import qualified Data.HashTable.Class as H (fromList)
import GHC.ST
import GHC.Magic (runRW# )
import Data.Maybe (fromMaybe)
import Data.Hashable (Hashable(..))

getBFstL' :: (Eq k, Hashable k) => v -> [(k, v)] -> k -> v
getBFstL' def pairs key = fromMaybe def
  ((\(ST st_rep) -> case runRW# st_rep of (# _, a #) -> a) . -- Actually is rewritten from the GHC.ST.runST to remove the forall constraint
    lookup2 pairs $ key)

lookup2 pairs key = H.fromList pairs >>= \ht -> C.lookup ht key
{-# INLINE lookup2 #-}