{-
Copyright (C) 2018 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 .
-}
{- |
[@AUTHOR@] Dr. Alistair Ward
[@DESCRIPTION@]
* .
* .
* .
* Valid move-sequences can be recorded against the hash of the position from which they start.
-}
module BishBosh.Search.Transpositions (
-- * Types
-- ** Type-synonyms
Transformation,
-- ** Data-types
Transpositions(),
-- * Functions
find,
-- ** Mutators
insert
) where
import qualified BishBosh.Property.Empty as Property.Empty
import qualified BishBosh.Search.EphemeralData as Search.EphemeralData
import qualified BishBosh.Search.TranspositionValue as Search.TranspositionValue
import qualified Data.Map
import qualified Data.Maybe
-- | Stores the result of an alpha-beta search from a /position/.
newtype Transpositions move positionHash = MkTranspositions {
deconstruct :: Data.Map.Map positionHash (Search.TranspositionValue.Value move)
}
instance Property.Empty.Empty (Transpositions move positionHash) where
empty = MkTranspositions Data.Map.empty
instance Search.EphemeralData.EphemeralData (Transpositions move positionHash) where
getSize MkTranspositions { deconstruct = byPositionHash } = Data.Map.size byPositionHash
euthanise nPlies MkTranspositions { deconstruct = byPositionHash } = MkTranspositions $ Data.Map.filter ((> nPlies) . Search.TranspositionValue.getNPlies) byPositionHash
-- | Returns any value previously recorded when searching from the specified /position/.
find
:: Ord positionHash
=> positionHash
-> Transpositions move positionHash
-> Maybe (Search.TranspositionValue.Value move)
find positionHash MkTranspositions { deconstruct = byPositionHash } = Data.Map.lookup positionHash byPositionHash
-- | The type of a function which transforms 'Transpositions'.
type Transformation move positionHash = Transpositions move positionHash -> Transpositions move positionHash
{- |
* Optionally record a value found while searching for the optimal move from a position, against the position's hash.
* If a matching key already exists, it's replaced if the new value is considered to be better.
-}
insert
:: (Ord positionHash, Ord weightedMean)
=> Search.TranspositionValue.FindFitness move weightedMean
-> positionHash -- ^ Represents the game from which the sequence of moves starts.
-> Search.TranspositionValue.Value move -- ^ The value to record.
-> Transformation move positionHash
insert findFitness positionHash proposedValue MkTranspositions { deconstruct = byPositionHash } = MkTranspositions $ Data.Map.alter (
Data.Maybe.maybe (Just proposedValue) {-there's no incumbent-} $ \incumbentValue -> if Search.TranspositionValue.isBetter findFitness proposedValue incumbentValue
then Just proposedValue -- Upgrade.
else Nothing -- Leave incumbent.
) positionHash byPositionHash