On 1/3/07, Neil Mitchell
As for beginner issues with rank-2 types, I've been learning Haskell for years now, and have never felt the need for a rank-2 type. If the interface for some feature requires rank-2 types I'd call that an abstraction leak in most cases. It certainly means that you can't properly Hoogle for it, can't compile it with Yhc, can't do full type inference etc.
That may well be true. Something I forgot to mention in my previous posting was that I'm not 100% convinced that the issue I hit with Takusen isn't a problem with the library - I find it very hard to read or understand some parts of the library documentation, basically because the types seem so complex. My intuition says that reading a database is logically similar to reading a file, so types like doQuery :: (Statement stmt sess q, QueryIteratee (DBM mark sess) q i seed b, IQuery q sess b) => stmt -> i -> seed -> DBM mark sess seed look pretty baffling to me - and don't match my intuition that main = do withSession (connect "user" "password" "server") $ do -- simple query, returning reversed list of rows. r <- doQuery (sql "select a, b, c from x") query1Iteratee [] liftIO $ putStrLn $ show r otherActions session is "basically I/O". (Oh, by the way - that "$" on the withSession line is the one that caused the error which started this thread...) Paul.