I once wrote a library typed-fsm https://github.com/sdzx-1/typed-fsm https://github.com/sdzx-1/typed-fsm It has a completely type-safe finite state machine, a

I once wrote a library typed-fsm https://github.com/sdzx-1/typed-fsm https://github.com/sdzx-1/typed-fsm It has a completely type-safe finite state machine, and it does not require additional programming conventions. It relies on a special monad: Mcbride Indexed Monad, which can model uncertainty in terms of type. Are you using this monad here? Here is a concrete ATM demo https://github.com/sdzx-1/typed-fsm/tree/main/examples/ATM https://github.com/sdzx-1/typed-fsm/tree/main/examples/ATM