[dullcrisp]

I might have this wrong but I think if you want state and exceptions you probably want StateT (ExceptT e m a). The alternative would be to have state or exceptions, i.e. when you have an exception you no longer have state (which might be a legitimate type in some cases).

[gloria_mundi]

Remember that transformers are "inside-out", i.e. `StateT (ExceptT e m) a` is isomorphic to `m (Except e (State a))`. If we want to keep state if an exception occurs, you need a `m (State (Except e a))` which is `ExceptT e (StateT m) a`.

[dullcrisp]

Yeah I could never keep this straight

[dllthomas]

The way I remembered it, before I internalized it, was to think about applying the run functions one at a time. runSomethingT will take a `SomethingT ... m ... a` and give you some kind of `m (... a)`.