Add concept of GameRoom, check viewing distance based on rooms

src/FoldableHelp.hs

@@ -2,14 +2,18 @@
 module FoldableHelp
     ( safeMinimumOn
     , safeMinimumOnMaybe
+    , safeMinimumOnMaybeF
+    , safeMinimumOnMaybeL
+    , safeMinMaybeL
     , module Data.Foldable
     )
     where
 import Data.Foldable
 
+import qualified Control.Foldl as L
 -- TODO check up whether and how it is necessary to specialise this
 -- | A version of 'minimum' where the comparison is done on some extracted value.
---   Returns Nothing if the list is empty. Only calls the function once per element (not true).
+--   Returns Nothing if the list is empty.
 --
 -- > safeMinimumOn id [] == Nothing
 -- > safeMinimumOn length ["test","extra","a"] == Just "a"
@@ -21,6 +25,34 @@ safeMinimumOn f = foldl' g Nothing
         | f x < f y = Just x
         | otherwise = Just y
     g Nothing y = Just y
+safeMinimumOnMaybeF :: (Ord b) => (a -> Maybe b) -> [a] -> Maybe a
+safeMinimumOnMaybeF f = L.fold $ L.Fold step initial extract
+  where
+    initial = Nothing
+    step Nothing      x  = (x ,) <$> f x
+    step (Just (a,x)) b = case f b of
+        Just y | y < x  -> Just (b,y)
+        _               -> Just (a,x)
+    extract = fmap fst
+safeMinMaybeL :: (Ord b) => (a -> Maybe b) -> L.Fold a (Maybe b)
+safeMinMaybeL f = L.Fold step initial id
+  where
+    initial = Nothing
+    step Nothing x  = f x
+    step (Just x) b = case f b of
+        Just y | y < x  -> Just y
+        _               -> Just x
+
+safeMinimumOnMaybeL :: (Ord b) => (a -> Maybe b) -> L.Fold a (Maybe a)
+safeMinimumOnMaybeL f = L.Fold step initial extract
+  where
+    initial = Nothing
+    step Nothing      x  = (x ,) <$> f x
+    step (Just (a,x)) b = case f b of
+        Just y | y < x  -> Just (b,y)
+        _               -> Just (a,x)
+    extract = fmap fst
+
 safeMinimumOnMaybe :: (Ord b) => (a -> Maybe b) -> [a] -> Maybe a
 safeMinimumOnMaybe f ys = fst <$> go Nothing ys
   where
@@ -29,6 +61,8 @@ safeMinimumOnMaybe f ys = fst <$> go Nothing ys
         Just v | v < cmin -> go (Just (x,v)) xs
         _                 -> go (Just (y,cmin)) xs
     go m _ = m
+
+
 --{- | Partial. -}
 --minimumOn :: Ord b => (a -> b) -> [a] -> a
 --minimumOn f [] = error "tried to take minimumOn of empty list"