Yep, it's an optional syntax sugar.
Indeed, you should use (contains? all-keys :baz) to check if :baz is
present in options. If :baz is present but it's value is nil,then (:baz
all-keys) returns nil too.
2014-08-18 18:57 GMT+08:00 Dave Tenny <dave.te...@gmail.com>:
> I don't think that a :p feature is necessary, since all you need to do to
> emulate it is a
> (:baz all-keys) to know if the user explicitly specified it. I.e. I think
> the capability is already present in adequate form but the documentation on
> map destructuring could be improved.
>
>
>
>
> On Sun, Aug 17, 2014 at 11:02 PM, dennis zhuang <killme2...@gmail.com>
> wrote:
>
>> 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
>> Email: killme2...@gmail.com xzhu...@avos.com
>> Site: http://fnil.net
>> Twitter: @killme2008
>>
>>
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>
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--
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Site: http://fnil.net
Twitter: @killme2008
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