> Do you want to mix differently typed Connections inside a single > transaction? It looks like you don't, so you may well leave out > existential types altogether and simply parametrize the Transaction > monad on the type of the connection it uses. > > data Connection c => TransactionState c = TS c > data Transaction c a = > Transaction (TransactionState c -> (a, TransactionState c) > > instance Monad (Transaction c) where ... > > getConnection :: Transaction c c > ... > > Note that Control.Monad.State does the same. > > Regards, > apfelmus
You are correct in that I don't want to mix different kind of connections inside a single transaction. I just didn't want to have to parameterize every single function using the monad. doSomething :: Transaction FirebirdConnection () doSomethingElse :: Transaction FirebirdConnection () Maybe I'm misunderstanding something but as I see it that would kind of stop me from running doSomething and doSomethingElse using different kinds of databases. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
