A little trouble upgrading to conduit 0.4.x

4 Apr 2012

      Hi all,

I'm upgrading various bits and bobs to conduit 0.4.x, but I've hit a 
little snag with "sourceStateIO". The following function fails to compile:
...
sourceQuery :: Database -> String -> [SQLData] -> Source IO [SQLData]
sourceQuery database sql parameters =
  sourceStateIO
  (do
      stmt <- SQL.prepare database sql
      return (Unbound,stmt))
  (\(_,stmt) -> SQL.finalize stmt)
  (\(state,stmt) -> do
      -- Bind parameters if necessary.
      when (state == Unbound) $ do
        SQL.bind stmt parameters
      -- Fetch results.
      nextResult <- SQL.step stmt
      case nextResult of
        Done -> return StateClosed
        Row -> liftM (StateOpen (Bound,stmt)) $ SQL.columns stmt)
All the SQL.xyz bits run in the IO monad. This code runs fine in Conduit 
0.2.x, but on Conduit 0.4.x it fails to compile with the following error:

src/Data/CQRS/EventStore/Backend/Sqlite3Utils.hs:43:3:
     No instance for 
(resourcet-0.3.2:Control.Monad.Trans.Resource.MonadResource
                        IO)
       arising from a use of `sourceStateIO'
     Possible fix:
       add an instance declaration for
       (resourcet-0.3.2:Control.Monad.Trans.Resource.MonadResource IO)
     In the expression:
       sourceStateIO
         [rest elided; just the rest of the definition of sourceQuery]
     In an equation for `sourceQuery':
         sourceQuery database sql parameters
           = sourceStateIO
		[rest elided; just the rest of the definition of sourceQuery]

I can see that I'm missing an instance, but I can't seem to find a 
direct instance for MonadResource IO, nor can I tell which indirect 
instance could get me there. I there some specific import I need to get 
the necessary instances, or do I need to do something else?

Regards,

Bardur Arantsson

Michael Snoyman

Bardur Arantsson

Michael Snoyman

Bardur Arantsson

Bardur Arantsson

Michael Snoyman

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