Hi,
Interesting. Seems more readable, more DRY, indeed. Especially if this
becomes idiomatic for optional named arguments ...
And the general case could be:
(defn funkymonkey [x y z & {:keys [[a -1] [b -2] [c -3]], d :d, e [:e
-4], :or {b -3, g -6}} [x y z a b c])
?
Which leads to the question: which default value "wins" for b ? :)
2010/3/24 Per Vognsen <per.vogn...@gmail.com>:
> Those of you following the clojure repo on GitHub may have noticed this
> commit:
>
> http://github.com/richhickey/clojure/commit/29389970bcd41998359681d9a4a20ee391a1e07c
>
> Now you can do things like this:
>
> user=> (defn funkymonkey [x y z & {:keys [a b c]}] [x y z a b c])
> #'user/funkymonkey
> user=> (funkymonkey 1 2 3)
> [1 2 3 nil nil nil]
> user=> (funkymonkey 1 2 3 :b 5)
> [1 2 3 nil 5 nil]
> user=> (funkymonkey 1 2 3 :c 6 :a 4 :b 5)
> [1 2 3 4 5 6]
>
> Very nice! It feels smoothly integrated with the general destructuring
> infrastructure. You can also supply default values with the :or
> binder:
>
> user=> (defn funkymonkey [x y z & {:keys [a b c] :or {a -1 b -2 c -3}]
> [x y z a b c])
> #'user/funkymonkey
> user=> (funkymonkey 1 2 3)
> [1 2 3 -1 -2 -3]
> user=> (funkymonkey 1 2 3 :b 5)
> [1 2 3 -1 5 -3]
>
> The great thing about :keys is that it cuts down on redundancy: you
> specify a symbol only once and it is dually interpreted as a map
> keyword and a lexically bound symbol. Since :keys already expects a
> flat sequence of symbols rather than arbitrary nested binding forms
> (otherwise this trick of dual interpretation wouldn't work), you could
> further cut down on the redundancy in the above :keys/:or idiom (which
> I expect would become commonplace with named arguments) by letting
> :keys elements optionally be two-element vectors with the second
> element supplying the default value:
>
> user=> (defn funkymonkey [x y z & {:keys [[a -1] [b -2] [c -3]]] [x y z a b
> c])
>
> What do you think? I hacked this into my local version of core.clj's
> destructure and it feels very natural to me.
>
> -Per
>
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