Paul Moore wrote:
db.hs:10:64: Couldn't match expected type `forall mark. DBM mark Session a' against inferred type `a1 b' In the second argument of `($)', namely `do r <- doQuery (sql "select username from all_users") query1Iteratee [] liftIO $ (putStrLn $ (show r))' In the expression: (withSession (connect "USER" "PASSWORD" "DB")) $ (do r <- doQuery (sql "select username from all_users") query1Iteratee [] liftIO $ (putStrLn $ (show r))) In the expression: do (withSession (connect "USER" "PASSWORD" "DB")) $ (do r <- doQuery (sql "select username from all_users") query1Iteratee [] liftIO $ (putStrLn $ (show r)))
I had the same problem... ($) doesn't have the expected semantics with existential types (like "forall mark. DBM mark Session a"). Some day I will be able to explain why this is so, but in the meantime, if you replace "liftIO $ putStrLn $ show r" with "liftIO (putStrLn (show r))", it should work.