On Wed, Aug 22, 2007 at 01:27:00PM -0500, Rich Neswold wrote:
>
> > newtype App a = App (ReaderT Connection (CGIT IO) a)
> >    deriving (Monad, MonadIO, MonadReader Connection)
>
> Unfortunately, when another module tries to actually use the monad, I
> get warnings about "No instance for (MonadCGI App)". I tried making an
> instance:
>
> > instance MonadCGI App where
> >     cgiAddHeader = ?
> >     cgiGet = ?

You have three choices:

1:

2:

3:
Provide a single instance for App that does the whole thing:
instance MonadCGI App where
    cgiAddHeader n v = App $ lift $ cgiAddHeader n v
    cgiGet x = App $ lift $ cgiGet x
This one you would obviously have to change if you added a StateT.