[Haskell-beginners] MonadThrow, MonadReader and shake

PICCA Frederic-Emmanuel frederic-emmanuel.picca at synchrotron-soleil.fr
Sat Dec 15 11:29:52 UTC 2018

> Hello,

Hello sylvain.

> The` toRuchePath` function has the following constraints on `m`:
> `MonadReader Beamline m, MonadThrow m`

> In your code, `m ~ Action` (from Shake) which doesn't fulfil the
> constraints (hence the error).


> If you want `m ~ ReaderT Beamline m IO`, you can use something like:
> `liftIO $ runReaderT stateBeforeCallingShake $ toRuchePath attachements`
> (you need `stateBeforeCallingShake <- ask` before calling shake).

ok, I will check this :).
Does it mean that if an instance of the MonadReader was writtent for shake (Action). it should work out of the box ?


More information about the Beginners mailing list