This is only allowed if there is a handler for all computation contexts the program could run in. In particular, if the program is in 'Eff' rather than 'EffT', then it is only valid for 'pure' handlers, like State. Note that, as a result, the effects a program can run isn't now limited to the top level set of effects. In the case of 'pure' effects, such as State or Rnd, I argue that this is okay. In the case of external effects such as IO related effects, you can only add effects if the top level context is impure. Again, I argue that this is okay - if you don't want to add impure effects, keep the top level context generic. Also added a test (by way of example) in effects004