{-# LANGUAGE CPP, FlexibleContexts #-}
{-
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@]
* Quantifies the fitness of a game.
* By measuring the fitness from the perspective of the player who just moved (rather than the next player to move),
an automated player can test various /move/s & select the fittest.
-}
module BishBosh.Evaluation.Fitness(
-- * Types
-- * Constants
-- maximumDestinations,
maximumDefended,
-- * Functions
measurePieceSquareValue,
measurePieceSquareValueIncrementally,
measureValueOfMaterial,
-- measureValueOfMobility,
measureValueOfCastlingPotential,
measureValueOfDefence,
measureValueOfDoubledPawns,
measureValueOfIsolatedPawns,
measureValueOfPassedPawns,
evaluateFitness
) where
import Control.Applicative((<|>))
import Control.Arrow((&&&))
import Data.Array.IArray((!))
import qualified BishBosh.Attribute.LogicalColour as Attribute.LogicalColour
import qualified BishBosh.Attribute.MoveType as Attribute.MoveType
import qualified BishBosh.Cartesian.Abscissa as Cartesian.Abscissa
import qualified BishBosh.Cartesian.Coordinates as Cartesian.Coordinates
import qualified BishBosh.Cartesian.Ordinate as Cartesian.Ordinate
import qualified BishBosh.Component.Move as Component.Move
import qualified BishBosh.Component.Piece as Component.Piece
import qualified BishBosh.Component.PieceSquareByCoordinatesByRank as Component.PieceSquareByCoordinatesByRank
import qualified BishBosh.Component.QualifiedMove as Component.QualifiedMove
import qualified BishBosh.Component.Turn as Component.Turn
import qualified BishBosh.Input.CriteriaWeights as Input.CriteriaWeights
import qualified BishBosh.Input.EvaluationOptions as Input.EvaluationOptions
import qualified BishBosh.Input.RankValues as Input.RankValues
import qualified BishBosh.Metric.CriterionValue as Metric.CriterionValue
import qualified BishBosh.Metric.WeightedMeanAndCriterionValues as Metric.WeightedMeanAndCriterionValues
import qualified BishBosh.Model.Game as Model.Game
import qualified BishBosh.Property.Opposable as Property.Opposable
import qualified BishBosh.Rule.GameTerminationReason as Rule.GameTerminationReason
import qualified BishBosh.State.Board as State.Board
import qualified BishBosh.State.CastleableRooksByLogicalColour as State.CastleableRooksByLogicalColour
import qualified BishBosh.Type.Count as Type.Count
import qualified BishBosh.Type.Mass as Type.Mass
import qualified Control.Monad.Reader
import qualified Data.Array.IArray
import qualified Data.Foldable
import qualified Data.List
import qualified Data.Map.Strict as Map
import qualified Data.Maybe
#ifdef USE_UNBOXED_ARRAYS
import qualified Data.Array.Unboxed
#endif
-- | Measures the piece-square value from the perspective of the last player to move.
measurePieceSquareValue :: (
#ifdef USE_UNBOXED_ARRAYS
Data.Array.Unboxed.IArray Data.Array.Unboxed.UArray pieceSquareValue, -- Requires 'FlexibleContexts'. The unboxed representation of the array-element must be defined (& therefore must be of fixed size).
#endif
Num pieceSquareValue
)
=> Component.PieceSquareByCoordinatesByRank.PieceSquareByCoordinatesByRank pieceSquareValue
-> Model.Game.Game
-> pieceSquareValue
{-# SPECIALISE measurePieceSquareValue :: Component.PieceSquareByCoordinatesByRank.PieceSquareByCoordinatesByRank Type.Mass.PieceSquareValue -> Model.Game.Game -> Type.Mass.PieceSquareValue #-}
measurePieceSquareValue pieceSquareByCoordinatesByRank game = (
if Attribute.LogicalColour.isBlack $ Model.Game.getNextLogicalColour game
then id
else negate -- Represent the piece-square value from Black's perspective.
) $ whitesPieceSquareValue - blacksPieceSquareValue where
[blacksPieceSquareValue, whitesPieceSquareValue] = Data.Array.IArray.elems . State.Board.sumPieceSquareValueByLogicalColour pieceSquareByCoordinatesByRank $ Model.Game.getBoard game
{- |
* Measures the piece-square value from the perspective of the last player to move.
* The previous value is provided, to enable calculation by difference.
* N.B.: because of diminishing returns, the piece-square value for everything but quiet moves is calculated from scratch.
-}
measurePieceSquareValueIncrementally :: (
#ifdef USE_UNBOXED_ARRAYS
Data.Array.Unboxed.IArray Data.Array.Unboxed.UArray pieceSquareValue, -- Requires 'FlexibleContexts'. The unboxed representation of the array-element must be defined (& therefore must be of fixed size).
#endif
Num pieceSquareValue
)
=> pieceSquareValue -- ^ The value before the last move was applied, & therefore also from the perspective of the previous player.
-> Component.PieceSquareByCoordinatesByRank.PieceSquareByCoordinatesByRank pieceSquareValue
-> Model.Game.Game
-> pieceSquareValue
{-# SPECIALISE measurePieceSquareValueIncrementally :: Type.Mass.PieceSquareValue -> Component.PieceSquareByCoordinatesByRank.PieceSquareByCoordinatesByRank Type.Mass.PieceSquareValue -> Model.Game.Game -> Type.Mass.PieceSquareValue #-}
measurePieceSquareValueIncrementally previousPieceSquareValue pieceSquareByCoordinatesByRank game
| Attribute.MoveType.isSimple $ Component.QualifiedMove.getMoveType qualifiedMove = let
findPieceSquareValue = uncurry (
Component.PieceSquareByCoordinatesByRank.findPieceSquareValue pieceSquareByCoordinatesByRank
) (
State.Board.getNPieces {- N.B.: no capture occurred-} . Model.Game.getBoard &&& Property.Opposable.getOpposite . Model.Game.getNextLogicalColour $ game {-the last player to move-}
) (
Component.Turn.getRank turn -- N.B.: no promotion occurred.
)
in uncurry (-) (
findPieceSquareValue . Component.Move.getDestination &&& findPieceSquareValue . Component.Move.getSource $ Component.QualifiedMove.getMove qualifiedMove
) - previousPieceSquareValue {-from the previous player's perspective-}
| otherwise = measurePieceSquareValue pieceSquareByCoordinatesByRank game -- N.B.: though non-simple (Castling, En-passant, promotion) can be calculated, the returns don't justify the effort.
where
Just turn = Model.Game.maybeLastTurn game
qualifiedMove = Component.Turn.getQualifiedMove turn
-- | Measure the arithmetic difference between the total /rank-value/ of the /piece/s currently held by either side; .
measureValueOfMaterial
:: Input.RankValues.RankValues
-> Type.Mass.RankValue -- ^ Maximum total rank-value.
-> Model.Game.Game
-> Metric.CriterionValue.CriterionValue
measureValueOfMaterial rankValues maximumTotalRankValue game = realToFrac . (
/ maximumTotalRankValue -- Normalise.
) . (
if Attribute.LogicalColour.isBlack $ Model.Game.getNextLogicalColour game
then id -- White just moved.
else negate -- Black just moved.
) . Data.List.foldl' (
\acc (rank, nPiecesDifference) -> if nPiecesDifference == 0
then acc -- Avoid calling 'Input.RankValues.findRankValue'.
else acc + realToFrac (
Input.RankValues.findRankValue rank rankValues
) * fromIntegral nPiecesDifference
) 0 . Data.Array.IArray.assocs . State.Board.getNPiecesDifferenceByRank {-which arbitrarily counts White pieces as positive & Black as negative-} $ Model.Game.getBoard game
{- |
* Count the difference between the reciprocals (cf. ), of the total number of /move/s available to each player.
* Using the reciprocal facilitates mapping into the /closed unit-interval/, & also emphasises the difference between having just one available move & having zero (i.e. mate).
In consequence, it is more about restricting the opponent's mobility (particularly the @King@) rather than increasing one's own.
This metric drives the game towards check-mate, rather than merely fighting a war of attrition.
* CAVEAT: avoiding a reduction of one's mobility to zero (i.e. mate) must be paramount => losing one's @Queen@ should be preferable.
measureValueOfMobility = 1 when mobility = 0, whereas loss of a @Queen@ = @ (rankValues ! Queen) / maximumTotalRankValue @,
=> getWeightOfMobility * 1 > weightOfMaterial * (8.8 / 102.47)
=> getWeightOfMobility > weightOfMaterial / 11.6
The corollary is that one probably shouldn't sacrifice even a @Knight@ to temporarily reduce one's opponent's mobility to one.
measureValueOfMobility = 0.5 when mobility = 1,
=> getWeightOfMobility * 0.5 < weightOfMaterial * (3.2 / 102.47)
=> getWeightOfMobility < weightOfMaterial / 16.0
CAVEAT: the loss of a @Knight@ occurs on the subsequent turn & is therefore downgraded, so even this represents too high a weighting.
This presents a paradox !
-}
measureValueOfMobility :: Model.Game.Game -> Metric.CriterionValue.CriterionValue
measureValueOfMobility game = realToFrac . uncurry (-) . (
measureConstriction &&& measureConstriction . Property.Opposable.getOpposite {-recent mover-}
) $ Model.Game.getNextLogicalColour game where
measureConstriction :: Attribute.LogicalColour.LogicalColour -> Type.Mass.CriterionValue
measureConstriction logicalColour = recip . fromIntegral {-NPlies-} . succ {-avoid divide-by-zero-} $ Model.Game.countPliesAvailableTo logicalColour game
-- | Measure the arithmetic difference between the potential to /Castle/, on either side.
measureValueOfCastlingPotential :: Model.Game.Game -> Metric.CriterionValue.CriterionValue
measureValueOfCastlingPotential game = realToFrac . uncurry (-) . (
castlingPotential . Property.Opposable.getOpposite {-recent mover-} &&& castlingPotential
) $ Model.Game.getNextLogicalColour game where
castlingPotential :: Attribute.LogicalColour.LogicalColour -> Type.Mass.CriterionValue
castlingPotential = Data.Maybe.maybe 1 {-have Castled-} (
(/ 2) . fromIntegral . length
) . (
`State.CastleableRooksByLogicalColour.locateForLogicalColour` Model.Game.getCastleableRooksByLogicalColour game
)
{- |
* Measure the arithmetic difference between the number of /doubled/ @Pawn@s on either side; .
* N.B.: measures tripled @Pawn@s as equivalent to two doubled @Pawn@s.
* CAVEAT: this is a negative attribute, so the weighted normalised value shouldn't exceed the reduction due to 'measureValueOfMaterial' resulting from a @Pawn@-sacrifice.
-}
measureValueOfDoubledPawns :: Model.Game.Game -> Metric.CriterionValue.CriterionValue
measureValueOfDoubledPawns game = realToFrac . (
/ (
6 :: Type.Mass.CriterionValue -- Normalise to [-1 .. 1]; the optimal scenario is all files containing one Pawn; the worst scenario is two files each containing four Pawns, all but one per file of which are counted as doubled.
)
) . fromIntegral {-NPieces-} . uncurry (-) . (
countDoubledPawns &&& countDoubledPawns . Property.Opposable.getOpposite {-recent mover-}
) $ Model.Game.getNextLogicalColour game where
countDoubledPawns :: Attribute.LogicalColour.LogicalColour -> Type.Count.NPieces
countDoubledPawns logicalColour = uncurry (-) . (
Data.Foldable.foldl' (+) 0 &&& fromIntegral . Data.Foldable.length {-one Pawn can't be considered to be doubled, so substract one Pawn per column-}
) $ State.Board.getNPawnsByFileByLogicalColour (Model.Game.getBoard game) ! logicalColour
{- |
* Measure the arithmetic difference between the number of /isolated/ @Pawn@s on either side; .
* CAVEAT: this is a negative attribute, so the weighted normalised value shouldn't exceed the reduction due to 'measureValueOfMaterial' resulting from a @Pawn@-sacrifice.
-}
measureValueOfIsolatedPawns :: Model.Game.Game -> Metric.CriterionValue.CriterionValue
measureValueOfIsolatedPawns game = realToFrac . (
/ (
fromIntegral {-X-} Cartesian.Abscissa.xLength :: Type.Mass.CriterionValue -- Normalise to [-1 .. 1]; the optimal scenario is eight files each containing one Pawn & the worst scenario is all Pawns isolated (e.g. 4 alternate files of 2, 2 separate files or 4, ...).
)
) . fromIntegral {-NPieces-} . uncurry (-) . (
countIsolatedPawns &&& countIsolatedPawns . Property.Opposable.getOpposite {-recent mover-}
) $ Model.Game.getNextLogicalColour game where
countIsolatedPawns :: Attribute.LogicalColour.LogicalColour -> Type.Count.NPieces
countIsolatedPawns logicalColour = Map.foldlWithKey' (
\acc x nPawns -> if (`Map.member` nPawnsByFile) `any` Cartesian.Abscissa.getAdjacents x
then acc -- This file has at least one neighbouring Pawn which can (if at a suitable rank) be used to protect any of those in this file.
else acc + nPawns -- All the Pawns on this file are isolated & thus lack the protection that may be offered by adjacent Pawns.
) 0 nPawnsByFile where
nPawnsByFile = State.Board.getNPawnsByFileByLogicalColour (Model.Game.getBoard game) ! logicalColour
-- | Measure the arithmetic difference between the number of /passed/ @Pawn@s on either side; .
measureValueOfPassedPawns :: Model.Game.Game -> Metric.CriterionValue.CriterionValue
measureValueOfPassedPawns game = realToFrac . (
/ fromIntegral {-X-} Cartesian.Abscissa.xLength -- Normalise to [-1 .. 1]; the optimal scenario is all files containing exactly one Pawn, of one's own logical colour, on the 7th rank.
) . uncurry (-) . (
valuePassedPawns . Property.Opposable.getOpposite {-recent mover-} &&& valuePassedPawns
) $ Model.Game.getNextLogicalColour game where
valuePassedPawns :: Attribute.LogicalColour.LogicalColour -> Type.Mass.CriterionValue
valuePassedPawns logicalColour = Data.List.foldl' (
\acc -> (acc +) . recip {-value increases exponentially as distance to promotion decreases-} . fromIntegral . abs . subtract (
Cartesian.Ordinate.lastRank logicalColour
) . Cartesian.Coordinates.getY -- Measure the distance to promotion.
) 0 $ State.Board.getPassedPawnCoordinatesByLogicalColour (Model.Game.getBoard game) ! logicalColour
{- |
* The constant maximum total number of times the /piece/s of either side, can be defended.
* Assumes all Pawns have been Queened.
* CAVEAT: assuming the optimal arrangement of pieces:
RQQB = 3 + 7 + 3 + 2 = 15
QQQN = 4 + 6 + 8 + 4 = 22
NQQK = 4 + 8 + 6 + 0 = 18
BQQR = 2 + 3 + 7 + 3 = 15
= 70
-}
maximumDefended :: Type.Count.NPieces
maximumDefended = 70
{- |
* Measure the normalised arithmetic difference between the number of /piece/s defending each of one's own, on either side.
* N.B. the /rank-value/ of the defended /piece/ is irrelevant because; it's the unknown value of the attacker that counts, since that's what the defender has the opportunity to counter-strike.
CAVEAT: the validity of this depends on the duration of the battle.
* N.B. defence of the @King@ is irrelevent, because it can't be taken.
* N.B. it's the total number of defenders which is relevant, rather than whether each piece has some protection, since it's not the individual battles but the war which counts.
* CAVEAT: this criterion competes with /mobility/, since each defended /piece/ blocks the path of the defender.
-}
measureValueOfDefence :: Model.Game.Game -> Metric.CriterionValue.CriterionValue
measureValueOfDefence game = realToFrac . (
/ (
fromIntegral {-NPieces-} maximumDefended :: Type.Mass.CriterionValue -- Normalise.
)
) . fromIntegral {-NPieces-} . uncurry (-) . (
(! Property.Opposable.getOpposite {-recent mover-} nextLogicalColour) &&& (! nextLogicalColour)
) . State.Board.summariseNDefendersByLogicalColour $ Model.Game.getBoard game where
nextLogicalColour = Model.Game.getNextLogicalColour game
{- |
* Evaluates the fitness of the /board/ from the perspective of the last player to move.
If the game has ended, the fitness is maximum for checkmate or zero for a draw,
but otherwise is the /weighted mean/ of various criteria; .
* Also returns the break-down of those /criterion-value/s with a non-zero /criterion-weight/.
* Besides measuring the difference between the total /rank-value/ on either side, other criteria are selected to represent known attributes of a good position.
* Many possible criteria aren't measured because they're, either currently or imminently, represented by those that are, typically by 'measureValueOfMaterial'.
-}
evaluateFitness :: (
#ifdef USE_UNBOXED_ARRAYS
Data.Array.Unboxed.IArray Data.Array.Unboxed.UArray pieceSquareValue, -- Requires 'FlexibleContexts'. The unboxed representation of the array-element must be defined (& therefore must be of fixed size).
#endif
Fractional pieceSquareValue,
Real pieceSquareValue
)
=> Maybe pieceSquareValue -- ^ An optional value for the specified game.
-> Model.Game.Game
-> Input.EvaluationOptions.Reader pieceSquareValue Metric.WeightedMeanAndCriterionValues.WeightedMeanAndCriterionValues
{-# SPECIALISE evaluateFitness :: Maybe Type.Mass.PieceSquareValue -> Model.Game.Game -> Input.EvaluationOptions.Reader Type.Mass.PieceSquareValue Metric.WeightedMeanAndCriterionValues.WeightedMeanAndCriterionValues #-}
evaluateFitness maybePieceSquareValue game
| Just gameTerminationReason <- Model.Game.getMaybeTerminationReason game = return {-to Reader-monad-} $ Metric.WeightedMeanAndCriterionValues.mkWeightedMeanAndCriterionValues (
if Rule.GameTerminationReason.isCheckMate gameTerminationReason
then 1 -- The last player to move, has won.
else 0 -- A draw.
) []
| otherwise = do
criteriaWeights <- Control.Monad.Reader.asks Input.EvaluationOptions.getCriteriaWeights
rankValuePair <- Control.Monad.Reader.asks $ Input.EvaluationOptions.getRankValues &&& Input.EvaluationOptions.getMaximumTotalRankValue
maybePieceSquareByCoordinatesByRank <- Control.Monad.Reader.asks Input.EvaluationOptions.getMaybePieceSquareByCoordinatesByRank
return {-to Reader-monad-} $ Input.CriteriaWeights.calculateWeightedMean criteriaWeights (
uncurry measureValueOfMaterial rankValuePair game
) (
measureValueOfMobility game
) (
Data.Maybe.maybe 0 (
realToFrac . (/ fromIntegral Component.Piece.nPiecesPerSide)
) $ maybePieceSquareValue <|> fmap (`measurePieceSquareValue` game) maybePieceSquareByCoordinatesByRank
) (
measureValueOfCastlingPotential game
) (
measureValueOfDefence game
) (
measureValueOfDoubledPawns game
) (
measureValueOfIsolatedPawns game
) (
measureValueOfPassedPawns game
)