@@ -24,7 +24,6 @@
2424
2525module Control.Monad.Unify where
2626
27−import Data.Maybe
2827import Data.String (IsString)
2928import Data.Monoid
3029
@@ -89,7 +88,7 @@ defaultUnifyState = UnifyState 0 mempty
8988-- The type checking monad, which provides the state of the type checker, and error reporting capabilities
9089--
9190newtype UnifyT t m a = UnifyT { unUnify :: (StateT (UnifyState t) m) a }
92− deriving (Functor, Monad, Applicative, MonadPlus)
91+ deriving (Functor, Monad, Applicative, Alternative, MonadPlus)
9392
9493instance (MonadState s m) => MonadState s (UnifyT t m) where
9594 get = UnifyT . lift $ get