I think that adding a :p option to destructuring would be great:
(let [ {:keys [a b c] :p {a a-p}} params]
(if a-p
(println a)
(println "a is not exists.")))
2014-08-17 20:05 GMT+08:00 Dave Tenny <dave.te...@gmail.com>:
> Well, it took me a while to perhaps get what you were telling me here.
>
> In my case I I had something like
>
> (defn foo [ & {:keys [bar ... more keys ...] :or {bar 1}} ] ...)
>
> and I wanted to know whether the user had explicilty invoked foo with :bar.
>
> What wasn't clear to me was that :as solved this problem.
> Reading http://clojure.org/special_forms#Special Forms--Binding Forms
> (Destructuring)-Map binding destructuring
> I guess I can see that it's telling me :as shows things that weren't in
> the init-form, but that's with hindsight.
>
> So, to emulated common lisp 'supplied-p' semantics, you can check the :as
> form, which will **not**
> contain :or values for keywords.
>
> E.g.
>
> user> (defn bar [ & {:keys [baz] :or {baz 'baz} :as all-keys} ] (println
> baz all-keys))
> #'user/bar
> user> (bar :bof 1)
> baz {:bof 1}
> nil
>
> And not that the all-keys form does not show a binding for baz, and that's
> what I wanted.
>
> Just fyi in case anybody searches topics for 'supplied-p' again.
>
>
> On Saturday, June 21, 2014 7:22:13 PM UTC-4, Jason Felice wrote:
>
>> If you destructure the parameters like this:
>> (defn f [& {:as a-map}] ...)
>>
>> You can use map primitives on a-map. But you can also supply defaults
>> here.
>> On Jun 20, 2014 2:14 PM, "Dave Tenny" <dave....@gmail.com> wrote:
>>
>>> What is the commonly accepted technique for declaring/using
>>> 'supplied-p' type lambda list functionality in clojure?
>>>
>>> http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/
>>> HyperSpec/Body/sec_3-4-1.html
>>>
>>>
>>> I have some clojure functions with a large number of keywords and
>>> various defaults, I want to know if a keyword was specified by the caller
>>> (rather than defaulted) in some cases.
>>>
>>> Certainly I could implement my own destructuring macros that did this,
>>> but I'd like to avoid reinventing a wheel here if I can, and also to know
>>> the idiomatic clojure way to do it.
>>>
>>> Thanks for any tips.
>>>
>>>
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庄晓丹
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Site: http://fnil.net
Twitter: @killme2008
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