runSymbol :: Eq a => Transducer a -> TransitionFunction a -> [a] -> StateTy ->
                 [Symbol a] -> Maybe [[a]]
runSymbol transducer _ [] s result
 | isFinal transducer s = Just [transform result]
 | otherwise            = Nothing
runSymbol :: Eq a => Transducer a -> TransitionFunction a -> [a] -> StateTy ->
                 [Symbol a] -> Maybe [[a]]
runSymbol transducer _ [] s result
 | isFinal transducer s = Just [transform result]
 | otherwise            = Nothing
runSymbol transducer _ [] s result
 | isFinal transducer s = Just [transform result]
 | otherwise            = Nothing