Re: [Haskell-cafe] Fighting the monad stack, MonadIO

On Apr 10, 2008, at 12:42 PM, Luke Palmer wrote:

On Thu, Apr 10, 2008 at 2:50 PM, Adam Smyczek wrote:

...

For a small webapi binding I try to implement a session like monad by building a stack including BrowserAction from Network.Browser module as following:

newtype RBAction a = RBAction { exec :: ErrorT String (StateT RBState BrowserAction) a } deriving (Functor, Monad, MonadState RBState)

I would like the RBAction to implement MonadIO as well, but fight with the liftIO function for hours now, without success. Any idea how the implementation of liftIO could look like?

I suspect BrowserAction does not implement MonadIO (lest you could just put MonadIO in the deriving clause). So, that depends on how BrowserAction is implemented. What package is Network.Browser in?

It's correct, BrowserAction does not implement MonadIO. This are the small things that confuse beginners like me :) Package http: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTTP-3001.0.4

Luke