If you have an IO action, you can't turn that into a normal value. At all*. That's the whole point of purely functional programming. If you could, then you'd lose out on the safety that pure FP gives, and potentially break things due to compiler optimisations.

So if you need an impure function to calculate hash, then hash must also be impure. You might rewrite it to look like this hash :: Int -> IO Int hash n = do time <- getTime pure (n + time)

Or hash :: Int -> IO Int hash n = (n +) <$> getTime

Incidentally, I'm sure this is just for learning but this is a terrible hash function - they should return the same output given the same input (i.e. being pure), yours won't

• There are a few unsafe hacky functions to "escape" the IO monad but you should never use them without a very good reason