src/Tools/Haskell/Haskell.thy

       case f x of
         Nothing -> get_aux (i + 1) xs
         Just y -> Just (i, y)
 
 separate :: a -> [a] -> [a]
-separate s (x : (xs @ (_ : _))) = x : s : separate s xs
+separate s (x : xs @ (_ : _)) = x : s : separate s xs
 separate _ xs = xs;
 
 
 {- strings -}