I'm using those watcher-fns that get called when the watched ref changes, and the watcher-fn gets passed the old-value and the new-value.
Now, nil is a proper value for a key-value and well as a val-value in a map, so passing nil does not give you the info whether or not an old-value existed or not, or whether a new-value is nil or no-value. With the getter fn: (get m k no-value-here), you have the option to pass this no-value-here argument which gets returned if there was no value - this allows you to distinguish nil from "no-value". However, in the watcher-fn you cannot pass such a no-value argument. One possible solution would be to define a well-know URI for the value of "no-value" - something like for example: "uri:http://clojure.org/uri/no-value";, or some other standardized constant. Any other/better suggestions? Thanks, FrankS. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
