Add airlocks

src/Dodge/RandomHelp.hs

@@ -41,7 +41,7 @@ takeN :: RandomGen g => Int -> [a] -> State g [a]
 takeN 0 xs = return []
 takeN i xs = fmap fst $ takeNMore i ([],xs)
 
--- to randomly shuffle a list
+-- | Randomly shuffle a list.
 shuffle :: RandomGen g => [a] -> State g [a]
 shuffle xs = do 
     let l = length xs
@@ -51,6 +51,10 @@ shuffle xs = do
     let (_,zs) = mapAccumR f xs rands
     return zs
 
+-- | Randomly shuffle the tail of a list, not safe.
+shuffleTail :: RandomGen g => [a] -> State g [a]
+shuffleTail (x:xs) = (x :) <$> shuffle xs
+
 randomSelectionFromList :: RandomGen g => Float -> [a] -> State g [a]
 randomSelectionFromList p = filterM $ const $ randProb p