[Haskell-beginners] testing IO code

[Maurizio Vitale]

suppose I have a restricted IO monad, RIO that only exposes readFile.
and then I have a monad SIO that will eventually provide a virtual file
system from a map path->content, also with a readFile function returning
SIO(String).

What is the way to write a function parseFile that can operate in both
monads so that I can use SIO for testing? should I define a third monad
CompileMonad that has instances for both RIO and SIO and then having
parseFile :: CompileMonad ast?

Thanks,

  Maurizio
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