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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