@@ -29,6 +29,7 @@ import Control.Monad.State.Strict
30import Data.Dependent.Sum (DSum (..))
30import Data.Dependent.Sum (DSum (..))
31import Data.Monoid
31import Data.Monoid
32+import Data.Traversable
32import Data.Maybe
33import Data.Maybe
33import qualified Data.IntMap.Strict as IntMap
34import qualified Data.IntMap.Strict as IntMap
34import Control.Monad.Ref
35import Control.Monad.Ref