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I didn't quite follow your comment. If the imperative solution tracks a list of changes why couldn't it implement infinite levels of undo in a similar fashion t

• dllthomas 13y ago
  It's a question of persistent data structures and sharing. Efficient code without mutability tends to recreate only the parts that change, and so you don't have to store a fresh copy of the whole world each update. Of course there is nothing preventing you from doing this in an imperative language, but a preference for mutability discourages it.