[htoolkit-users] Design question of Connection from HSQL

[Marc W. <mar...@gm...>]

Connection is definied as follows:

database, through which you can operate on the it.
-- In order to create the connection you need to use the @connect@ function from the module for
-- your prefered backend.
data Connection
  =  Connection
		{ connDisconnect :: IO ()
		, connExecute :: String -> IO Integer
		, connPrepare :: String -> IO Statement
		, connQuery :: String -> IO Statement
		, connTables :: IO [String]
		, connDescribe :: String -> IO [FieldDef]
		, connBeginTransaction :: IO ()
		, connCommitTransaction :: IO ()
		, connRollbackTransaction :: IO ()
		, connClosed :: MVar Bool
		}
So it's actually a record containing mostly IO () values? (or functions
with this return value? ) It doesn't matter because the IO () results
aren't evaluated as long as they aren't needed, right?

Would it be equivalent to have some kind of class design:

class Connection c where
  connDisconnect :: c -> ()
  connPrepare :: c -> String -> IO Integer
  [...]

with an implementation for each kind of Database connection handle?
EG:
Data MySQLhandle=MySQLhandle Int

instance MySQLhandle handle where
  connDisconnect  c = MySQLCloseHandle $ MySQLhandle c
  [ ... ] ?

The way it's implemented the connect function of MySQL simply adds this
handle to every functions as argument:

  [...]
	let connection = Connection
		{ connDisconnect = mysql_close pMYSQL
		, connExecute = execute pMYSQL
		, connQuery = query connection pMYSQL
		, connTables = tables connection pMYSQL
		, connDescribe = describe connection pMYSQL
		, connBeginTransaction = execute pMYSQL "begin" >> return ()
		, connCommitTransaction = execute pMYSQL "commit" >> return ()
		, connRollbackTransaction = execute pMYSQL "rollback" >> return ()
		, connClosed = refFalse
		}
	return connection
	where
	[...]

In my imaginated case the connect method would just return the Database
handle.

Where is the difference?

Marc