I'm playing around with a little program that implements a simple virtual
machine. I want to use a monad to represent machine state. I created a data
type for the machine (VM) and a monadic type for the monadic computations using
it. I declared this an instance of MonadState and Monad and created the usual
operators. That stuff works. My issue is that I want to run some functions in
the machine monad, call it VMS - "virtual machine w/state" and then pull the
underlying VM data structure out and print it.
I've read about monad transformers, lift, liftM, liftIO and all these instances
in the libraries like MonadIO and am rather confused. The most sensible
conclusion I can reach is that I probably need to create my own Transformer
monad and define liftIO. Is this where I need to go? Also, my VMS monad
doesn't really do anything different from the State monad except explicitly
specify that state is a VM and not a generic type. Am I doing too much work
creating my own instances here? Would a simple "type" statement work?
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