Hashable.hs

{-
	Copyright (C) 2021 Dr. Alistair Ward

	This file is part of BishBosh.

	BishBosh is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	BishBosh is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with BishBosh.  If not, see <http://www.gnu.org/licenses/>.
-}
{- |
 [@AUTHOR@]	Dr. Alistair Ward

 [@DESCRIPTION@]

	* Defines the random-numbers required to construct a hash of a chess-position.

	* Facilitates the construction of a hash from arbitrary data.
-}

module BishBosh.StateProperty.Hashable(
-- * Type-classes
	Hashable(..),
-- * Constants
--	combiningOp,
-- * Functions
	hash,
	combine
) where

import qualified	BishBosh.Component.Zobrist	as Component.Zobrist
import qualified	Data.Bits
import qualified	Data.List

-- | An interface to which hashable data can conform.
class Hashable hashable where
	listRandoms	:: hashable -> Component.Zobrist.Zobrist positionHash -> [positionHash]

-- | The operator used when combining random numbers to compose a hash.
combiningOp :: Data.Bits.Bits positionHash => positionHash -> positionHash -> positionHash
combiningOp	= Data.Bits.xor

-- | Resolve a hashable into a hash.
hash :: (
	Data.Bits.Bits	positionHash,
	Hashable	hashable
 )
	=> hashable
	-> Component.Zobrist.Zobrist positionHash
	-> positionHash
hash hashable	= Data.List.foldl1' combiningOp . listRandoms hashable

-- | Include a list of random numbers in the hash.
combine :: Data.Bits.Bits positionHash => positionHash -> [positionHash] -> positionHash
combine	= Data.List.foldl' combiningOp