Tweak inventory management

src/ListHelp.hs

@@ -2,6 +2,7 @@ module ListHelp
     (module Data.List
     ,initOrNull
     , insertOver
+    , swapIndices
     )where
 import Data.List
 
@@ -11,3 +12,6 @@ initOrNull xs = init xs
 
 insertOver :: Int -> a -> [a] -> [a]
 insertOver i x xs = take i xs ++ x : drop (i+1) xs
+
+swapIndices :: Int -> Int -> [a] -> [a]
+swapIndices i j xs = insertOver i (xs !! j) . insertOver j (xs !! i) $ xs