implement `catchDynE` to catch errors without losing the other effects state

[Serhii Khoma]

I didnt find this function in https://hackage.haskell.org/package/freer

but it was in a paper "Freer Monads, More Extensible Effects" http://okmij.org/ftp/Haskell/extensible/more.pdf

it allows catching IO exceptions in the presence of other effects

---

current behaviour is

main = do
  (result :: Either Error Unit) <- Run.runBaseEffect $ runExcept $ do
    Run.catch (errorHander) (Run.liftEffect $ throwError $ error "asdf")
  traceM { result }

will throw runtime error "asdf" and the { result } is not printed

expected: replace Run.catch with Run.catchDynE and catch the js error, print { result } and finish without error code

[Serhii Khoma]

another example

output <- runEffect $ runWriter "" do
  write "1"
  catchDynE (\e -> write "error catched") do
    write "2"
    liftEffect $ throw $ error "myerror"
    write "3"
  write "4"

output `shouldEqual` "12error catched4"

[Nathan Faubion]

I think some kind of function like this is useful, but what do you expect the type signature to be? Exceptions in PureScript and exceptions in Haskell are not the same.

[Nathan Faubion]

Is this better handled at the lift layer?

liftAff' = rethrow <=< liftAff <<< attempt