Add concept of GameRoom, check viewing distance based on rooms

src/FoldlHelp.hs

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+module FoldlHelp
+    ( minimumOn
+    , premapMaybe
+    , module Control.Foldl
+    )
+    where
+import Control.Foldl
+
+data Maybe' a = Just' !a | Nothing'
+data Pair a b = !a :!: !b
+
+minimumOn :: Ord b => (a -> b) -> Fold a (Maybe a)
+minimumOn f = Fold step Nothing' extract
+  where
+    extract Nothing' = Nothing
+    extract (Just' (a :!: _)) = Just a
+    step Nothing' b = Just' (b :!: f b)
+    step (Just' (a :!: x)) b
+        | y < x     = Just' (b :!: y)
+        | otherwise = Just' (a :!: x)
+      where
+        y = f b
+
+premapMaybe :: (a -> Maybe b) -> Fold b r -> Fold a r
+{-# INLINABLE premapMaybe #-}
+premapMaybe f (Fold step initial extract) = Fold step' initial extract
+  where
+    step' x a = case f a of
+        Nothing -> x
+        Just s  -> step x s