Fix inventory swapping equipment bug

src/IntMapHelp.hs

@@ -3,9 +3,11 @@ module IntMapHelp
     , newKey
     , insertNewKey
     , insertWithNewKeys
-    , swapKeys
+    , unsafeSwapKeys
+    , safeSwapKeys
     , findIndex
     ) where
+import LensHelp
 --import Data.List hiding (foldr,insert)
 import Data.IntMap.Strict
 {- | Find a key value one higher than any key in the map, or zero if the map is
@@ -21,8 +23,13 @@ insertNewKey x m = case lookupMax m of
 insertWithNewKeys :: [a] -> IntMap a -> IntMap a
 insertWithNewKeys xs m = union m $ fromList $ zip [newKey m..] xs
 {- | Swaps two keys. Unsafe: assumes both keys exist. -}
-swapKeys :: Int -> Int -> IntMap a -> IntMap a
-swapKeys i j m = insert i (m ! j) $ insert j (m ! i) m
+unsafeSwapKeys :: Int -> Int -> IntMap a -> IntMap a
+unsafeSwapKeys i j m = insert i (m ! j) $ insert j (m ! i) m
+
+safeSwapKeys :: Int -> Int -> IntMap a -> IntMap a
+safeSwapKeys i j m = m
+    & at i .~ (m ^? ix j)
+    & at j .~ (m ^? ix i)
 
 -- ideally this should short circuit, I am not sure whether it does or not
 -- though