Try to fix my own function but still does'nt work

anagram.hs

@@ -2,7 +2,7 @@ import Data.List
 
 sweep::(String -> [String]) -> String -> String -> [String]
 sweep f l stack = case stack of
-	[] -> [l]
+	[] -> [""]
 	cur:substack -> concat [map (\xs -> cur:xs) (f (delete cur l)), sweep f l substack]
 
 ana::String -> [String]