The equivalent Haskell program is

    import Data.IORef

    main :: IO ()
    main = do
        r <- newIORef []
        writeIORef r ["Hello"]
        x <- readIORef r
        print $ x + 1
        return () 

The reference is bound by "r <-", ie a lambda (as this desugars to ">>= \ r ->"), and lambdas are never generalized (even in ocaml).

I think that the reason why it works is that because there is no way to let-bind r except with a toplevel unsafePerformIO.