On 1/3/07, Neil Mitchell <[EMAIL PROTECTED]> wrote:
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.
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