Tom Pledger wrote:
How about introducing a Cursor abstract data type?
doquery :: Process -> String -> b -> (Cursor -> b -> IO (b, Bool)) -> IO b stringv :: Cursor -> CInt -> IO String doublev :: Cursor -> CInt -> IO Double intv :: Cursor -> CInt -> IO Int
This achieves the restriction you're after, because doquery is the only exported producer of Cursor, and stringv etc. are the only exported consumers of Cursor.
I like this. Not sure about whether I'd call it Cursor or just Row. Code something like results <- doquery dbconn sqltext [] \row results -> do name <- colv row 1 address <- colv row 2 return (name,address):results seems quite tidy.
It also has the benefit that the function you pass to doquery can make other calls to doquery, without mucking up the 'current row' state. There would be one current row per Cursor, not one per Process.
Is it normal or common to support multiple simultaneous queries on a single DB connection? Tim