Now that I'm done putting 900 miles on my odometer, let me expand on that. The ST monad is not the answer. If you're writing code and suddenly you realize you

Now that I'm done putting 900 miles on my odometer, let me expand on that. The ST monad is not the answer. If you're writing code and suddenly you realize you need to modify state, there's a big difference between adding a variable, and rewriting the whole thing to sit inside the ST monad. And if you put everything inside the ST monad in the first place, you're working with a much more cumbersome imperative language than one where you have to write newSTRef for every variable you create.