5 files changed, 125 insertions, 53 deletions
diff --git a/users/grfn/xanthous/src/Xanthous/Game/Arbitrary.hs b/users/grfn/xanthous/src/Xanthous/Game/Arbitrary.hs
index 1b15ad4ffa64..bb9b64b0b303 100644
--- a/users/grfn/xanthous/src/Xanthous/Game/Arbitrary.hs
+++ b/users/grfn/xanthous/src/Xanthous/Game/Arbitrary.hs
@@ -42,6 +42,7 @@ instance Arbitrary GameState where
     _activePanel <- arbitrary
     _debugState <- arbitrary
     let _autocommand = NoAutocommand
+    _memo <- arbitrary
     pure $ GameState {..}
 
 
diff --git a/users/grfn/xanthous/src/Xanthous/Game/Draw.hs b/users/grfn/xanthous/src/Xanthous/Game/Draw.hs
index 2375ae8c557e..14d2dcd22cd5 100644
--- a/users/grfn/xanthous/src/Xanthous/Game/Draw.hs
+++ b/users/grfn/xanthous/src/Xanthous/Game/Draw.hs
@@ -23,6 +23,8 @@ import           Xanthous.Game
                  )
 import           Xanthous.Game.Prompt
 import           Xanthous.Orphans ()
+import Control.Monad.State.Lazy (evalState)
+import Control.Monad.State.Class ( get, MonadState, gets )
 --------------------------------------------------------------------------------
 
 cursorPosition :: GameState -> Widget ResourceName -> Widget ResourceName
@@ -53,29 +55,28 @@ drawPromptState (WaitingPrompt msg (Prompt _ pt ps pri _)) =
       str ("[" <> pure chr <> "] ") <+> txtWrap m
 
 drawEntities
-  :: GameState
-  -> Widget ResourceName
-drawEntities game = vBox rows
-  where
-    allEnts = game ^. entities
-    entityPositions = EntityMap.positions allEnts
-    maxY = fromMaybe 0 $ maximumOf (folded . y) entityPositions
-    maxX = fromMaybe 0 $ maximumOf (folded . x) entityPositions
-    rows = mkRow <$> [0..maxY]
-    mkRow rowY = hBox $ renderEntityAt . flip Position rowY <$> [0..maxX]
-    renderEntityAt pos
-      = renderTopEntity pos $ revealedEntitiesAtPosition pos game
-    renderTopEntity pos ents
-      = let neighbors = EntityMap.neighbors pos allEnts
-        in maybe (str " ") (drawWithNeighbors neighbors)
-           $ maximumBy (compare `on` drawPriority)
-           <$> fromNullable ents
+  :: forall m. MonadState GameState m
+  => m (Widget ResourceName)
+drawEntities = do
+  allEnts <- use entities
+  let entityPositions = EntityMap.positions allEnts
+      maxY = fromMaybe 0 $ maximumOf (folded . y) entityPositions
+      maxX = fromMaybe 0 $ maximumOf (folded . x) entityPositions
+      rows = traverse mkRow [0..maxY]
+      mkRow rowY = hBox <$> traverse (renderEntityAt . flip Position rowY) [0..maxX]
+      renderEntityAt pos
+        = renderTopEntity pos <$> revealedEntitiesAtPosition pos
+      renderTopEntity pos ents
+        = let neighbors = EntityMap.neighbors pos allEnts
+          in maybe (str " ") (drawWithNeighbors neighbors)
+             $ maximumBy (compare `on` drawPriority)
+             <$> fromNullable ents
+  vBox <$> rows
 
-drawMap :: GameState -> Widget ResourceName
-drawMap game
-  = viewport Resource.MapViewport Both
-  . cursorPosition game
-  $ drawEntities game
+drawMap :: MonadState GameState m => m (Widget ResourceName)
+drawMap = do
+  cursorPos <- gets cursorPosition
+  viewport Resource.MapViewport Both . cursorPos <$> drawEntities
 
 bullet :: Char
 bullet = '•'
@@ -129,15 +130,18 @@ drawCharacterInfo ch = txt " " <+> charName <+> charHitpoints
       <+> txt (tshow $ let Hitpoints hp = characterHitpoints ch in hp)
 
 drawGame :: GameState -> [Widget ResourceName]
-drawGame game
-  = pure
-  . withBorderStyle unicode
-  $ case game ^. promptState of
-       NoPrompt -> drawMessages (game ^. messageHistory)
-       _ -> emptyWidget
-  <=> drawPromptState (game ^. promptState)
-  <=>
-  (maybe emptyWidget (drawPanel game) (game ^. activePanel)
-  <+> border (drawMap game)
-  )
-  <=> drawCharacterInfo (game ^. character)
+drawGame = evalState $ do
+  game <- get
+  drawnMap <- drawMap
+  pure
+    . pure
+    . withBorderStyle unicode
+    $ case game ^. promptState of
+        NoPrompt -> drawMessages (game ^. messageHistory)
+        _ -> emptyWidget
+    <=> drawPromptState (game ^. promptState)
+    <=>
+    (maybe emptyWidget (drawPanel game) (game ^. activePanel)
+    <+> border drawnMap
+    )
+    <=> drawCharacterInfo (game ^. character)
diff --git a/users/grfn/xanthous/src/Xanthous/Game/Lenses.hs b/users/grfn/xanthous/src/Xanthous/Game/Lenses.hs
index 6242b855f1cc..d93d30aba876 100644
--- a/users/grfn/xanthous/src/Xanthous/Game/Lenses.hs
+++ b/users/grfn/xanthous/src/Xanthous/Game/Lenses.hs
@@ -27,6 +27,7 @@ import           Control.Monad.State
 import           Control.Monad.Random (getRandom)
 --------------------------------------------------------------------------------
 import           Xanthous.Game.State
+import qualified Xanthous.Game.Memo as Memo
 import           Xanthous.Data
 import           Xanthous.Data.Levels
 import qualified Xanthous.Data.EntityMap as EntityMap
@@ -35,6 +36,8 @@ import           Xanthous.Data.EntityMap.Graphics
 import           Xanthous.Data.VectorBag
 import           Xanthous.Entities.Character (Character, mkCharacter)
 import           {-# SOURCE #-} Xanthous.Entities.Entities ()
+import Xanthous.Game.Memo (emptyMemoState)
+import Xanthous.Data.Memo (fillWithM)
 --------------------------------------------------------------------------------
 
 getInitialState :: IO GameState
@@ -60,9 +63,9 @@ initialStateFromSeed seed =
         { _allRevealed = False
         }
       _autocommand = NoAutocommand
+      _memo = emptyMemoState
   in GameState {..}
 
-
 positionedCharacter :: Lens' GameState (Positioned Character)
 positionedCharacter = lens getPositionedCharacter setPositionedCharacter
   where
@@ -96,13 +99,17 @@ visionRadius = 12 -- TODO make this dynamic
 -- | Update the revealed entities at the character's position based on their
 -- vision
 updateCharacterVision :: GameState -> GameState
-updateCharacterVision game
-  = game & revealedPositions <>~ characterVisiblePositions game
-
-characterVisiblePositions :: GameState -> Set Position
-characterVisiblePositions game =
-  let charPos = game ^. characterPosition
-  in visiblePositions charPos visionRadius $ game ^. entities
+updateCharacterVision = execState $ do
+  positions <- characterVisiblePositions
+  revealedPositions <>= positions
+
+characterVisiblePositions :: MonadState GameState m => m (Set Position)
+characterVisiblePositions = do
+  charPos <- use characterPosition
+  fillWithM
+    (memo . Memo.characterVisiblePositions)
+    charPos
+    (uses entities $ visiblePositions charPos visionRadius)
 
 characterVisibleEntities :: GameState -> EntityMap.EntityMap SomeEntity
 characterVisibleEntities game =
@@ -137,14 +144,18 @@ entitiesAtCharacter = lens getter setter
 -- Concretely, this is either entities that are *currently* visible to the
 -- character, or entities, that are immobile and that the character has seen
 -- before
-revealedEntitiesAtPosition :: Position -> GameState -> (VectorBag SomeEntity)
-revealedEntitiesAtPosition p gs
-  | p `member` characterVisiblePositions gs
-  = entitiesAtPosition
-  | p `member` (gs ^. revealedPositions)
-  = immobileEntitiesAtPosition
-  | otherwise
-  = mempty
-  where
-    entitiesAtPosition = gs ^. entities . EntityMap.atPosition p
-    immobileEntitiesAtPosition = filter (not . entityCanMove) entitiesAtPosition
+revealedEntitiesAtPosition
+  :: MonadState GameState m
+  => Position
+  -> m (VectorBag SomeEntity)
+revealedEntitiesAtPosition p = do
+  cvps <- characterVisiblePositions
+  entitiesAtPosition <- use $ entities . EntityMap.atPosition p
+  revealed <- use revealedPositions
+  let immobileEntitiesAtPosition = filter (not . entityCanMove) entitiesAtPosition
+  pure $ if | p `member` cvps
+              -> entitiesAtPosition
+            | p `member` revealed
+              -> immobileEntitiesAtPosition
+            | otherwise
+              -> mempty
diff --git a/users/grfn/xanthous/src/Xanthous/Game/Memo.hs b/users/grfn/xanthous/src/Xanthous/Game/Memo.hs
new file mode 100644
index 000000000000..9e483a8d4af7
--- /dev/null
+++ b/users/grfn/xanthous/src/Xanthous/Game/Memo.hs
@@ -0,0 +1,52 @@
+{-# 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) #-}
diff --git a/users/grfn/xanthous/src/Xanthous/Game/State.hs b/users/grfn/xanthous/src/Xanthous/Game/State.hs
index f614cad47339..cdaf23edcd48 100644
--- a/users/grfn/xanthous/src/Xanthous/Game/State.hs
+++ b/users/grfn/xanthous/src/Xanthous/Game/State.hs
@@ -16,6 +16,7 @@ module Xanthous.Game.State
   , promptState
   , characterEntityID
   , autocommand
+  , memo
   , GamePromptState(..)
 
     -- * Game Level
@@ -107,6 +108,7 @@ import           Xanthous.Data.Entities
 import           Xanthous.Orphans ()
 import           Xanthous.Game.Prompt
 import           Xanthous.Game.Env
+import           Xanthous.Game.Memo (MemoState)
 --------------------------------------------------------------------------------
 
 data MessageHistory
@@ -502,6 +504,8 @@ data GameState = GameState
   , _promptState       :: !(GamePromptState AppM)
   , _debugState        :: !DebugState
   , _autocommand       :: !AutocommandState
+
+  , _memo              :: MemoState
   }
   deriving stock (Show, Generic)
   deriving anyclass (NFData)