[Haskell-cafe] Re: Foralls in records

[Martin Huschenbett]

Hi,

instead of writing a function getTransaction that retrieves the 
connection you could write a function withConnection that doesn't return 
the connection itself but performs an operation on the connection:

withConnection ::
	(forall c. Connection c => c -> Transaction a) -> Transaction a
withConnection f = Transaction (\t@(TransactionT c) ->
	let Transaction tf = f c in tf t)

Then execute becomes:

execute :: String -> Transaction ()
execute s = withConnection (\c -> connectionExecute c s)


Regards,
   Martin.


> getConnection :: Transaction c
> getConnection = Transaction (\t@(TransactionT c) -> (c, t))
> 
> class Connection c where
>   connectionExecute :: c -> String -> Transaction ()
> 
> execute :: String -> Transaction ()
> execute s = connectionExecute getConnection s