how to return error with data from Aff

[harrhp]

Right now i usually return EitherAsync<AppError, A> from my services,

interface AppError {}

record AppError1 : AppError;

record AppError2(string SomeValue) : AppError;

so in controller i can match on either and switch on error type to access properties in AppError2 case. I've read wiki about Aff, but there is no example of returning error with data. The only way i see how to achieve this with Error is to convert my AppErrors to Exceptions. Is this ok or there is something better? Maybe there should be @catch overload

public static CatchValue<A> @catch<A>(Func<Exception, Option<Fin<A>>> Fail);

if possible to be able to handle different exception types differently and require downcast only in one place?

[louthy]

It is an intentional limitation of the Aff/Eff implementation, because it would mean another 4 monads (to support an E error type). And whilst I'm not against that idea, the amount of typing to get to this point has been enormous, and I'm not sure I've got the energy to do another four monads on-top of the core four monads (at least, not any time soon).

So, yes, the only way to leverage the Error type as it stands right now is to make AppError into an:

    abstract class AppError : Exception

It does unfortunately mean dropping the use of records, which granted isn't great.