On Mar 19, 2012, at 5:31 PM, Michael Gardner wrote:
> Or the simplest option: just have your functions return nil to indicate that
> the world state should remain unchanged from its previous value.
If your world state is a hash-map, you could also return partial states and
merge them into the existing world; that would make nil automatically mean "no
change". Let's say your world has the key :player (among other things):
(defn move-player [{:keys [player ...]} ...]
(when (can-move player)
{:player (assoc player ...)}))
The above returns nil when (can-move player) returns false; otherwise it
returns a hash-map with only the key :player defined. Then (merge world
(move-player world ...)) does the right thing, with no special-casing of nil
needed.
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