I must be missing the point here because if you wanted to “write ... Haskell using only the IO monad and modules of functions” you could simply write your modul

I must be missing the point here because if you wanted to “write ... Haskell using only the IO monad and modules of functions” you could simply write your modules (Haskell supports modules) and then write your IO. Done. Is that what you mean? Or is this really about something else?