Isaac Dupree schrieb:
apfelmus wrote:
Mutable data structures in the sense of ephemeral (= not persistent = update in-place) data structure indeed do introduce the need to work in ST since the old version is - by definition - not available anymore.
Not in the quantum/information-theoretic sense, not necessarily. Consider
import Control.Monad.ST import Data.STRef main = print (runST (do r <- newSTRef 1 notUnavailable <- readSTRef r writeSTRef r 5 return notUnavailable ))
I'm not sure what this has to do with quantum mechanics ;) but you're right, I forgot that. This means that either STRefs cannot be updated in-place or that every read operation copies the contents or something like that. In any case, simple values like Ints or Bools are rather uninteresting, update in-place is only important for larger structures like arrays. Here, ST does updates in-place and retaining an array will copy it. Regards, apfelmus