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+{-# LANGUAGE TemplateHaskell #-}
+--------------------------------------------------------------------------------
+-- | Memoized versions of calculations
+--------------------------------------------------------------------------------
+module Xanthous.Game.Memo
+  ( MemoState
+  , emptyMemoState
+  , clear
+    -- ** Memo lenses
+  , characterVisiblePositions
+
+    -- * Memoized values
+  , Memoized(UnMemoized)
+  , memoizeWith
+  , getMemoized
+  , runMemoized
+  ) where
+--------------------------------------------------------------------------------
+import Xanthous.Prelude
+--------------------------------------------------------------------------------
+import Data.Aeson (ToJSON, FromJSON)
+import Data.Aeson.Generic.DerivingVia
+import Test.QuickCheck (CoArbitrary, Function, Arbitrary)
+--------------------------------------------------------------------------------
+import Xanthous.Data (Position)
+import Xanthous.Data.Memo
+import Xanthous.Util.QuickCheck (GenericArbitrary(GenericArbitrary))
+--------------------------------------------------------------------------------
+
+-- | Memoized calculations on the game state
+data MemoState = MemoState
+  { -- | Memoized version of 'Xanthous.Game.Lenses.characterVisiblePositions',
+    -- memoized with the position of the character
+    _characterVisiblePositions :: Memoized Position (Set Position)
+  }
+  deriving stock (Show, Eq, Generic)
+  deriving anyclass (NFData, CoArbitrary, Function)
+  deriving Arbitrary via GenericArbitrary MemoState
+  deriving (ToJSON, FromJSON)
+       via WithOptions '[ FieldLabelModifier '[Drop 1] ]
+           MemoState
+makeLenses ''MemoState
+
+emptyMemoState :: MemoState
+emptyMemoState = MemoState { _characterVisiblePositions = UnMemoized }
+{-# INLINE emptyMemoState #-}
+
+clear :: Lens' MemoState (Memoized k v) -> MemoState -> MemoState
+clear = flip set UnMemoized
+{-# INLINE clear #-}
+
+{-# ANN module ("Hlint: ignore Use newtype instead of data" :: String) #-}