@@ -40,6 +40,8 @@ type DbConn = (C.SessionId, C.Connection)
4040newtype Db a = Db {runDb :: ReaderT DbConn IO a}
4141 deriving (Functor, Applicative, Monad, MonadIO)
4242
43+-- This exception type should never be observable by the API users.
44+-- It merely carries errors which end up as RelError at the end of a transaction.
4345newtype TransactionCancelled = TransactionCancelled DbError deriving Show
4446instance Exception TransactionCancelled
4547