mapSymbolsT :: (Monad m, Monad n) =>
               (m a -> n b) -> SymbolsT m a -> SymbolsT n b
mapSymbolsT f = SymbolsT . mapReaderT f . unpackSymbolsT
mapSymbolsT :: (Monad m, Monad n) =>
               (m a -> n b) -> SymbolsT m a -> SymbolsT n b
mapSymbolsT f = SymbolsT . mapReaderT f . unpackSymbolsT
mapSymbolsT f = SymbolsT . mapReaderT f . unpackSymbolsT