As I understand it, a function use :: Item -> Item in Haskell guarantees that it can't change any property of any item;even more so if the function were use :: Item -> Effect, as could be done on the initial assumption that Items can't change.
In general you can't mutate records. Nothing prevents you from making a new one that's slightly different though. It just won't change the already existing one.
In practice this is not actually a problem. It just takes a little getting used to to get yourself out of the 'memory-address as identity' mindset that procedural languages have.
