Aha, got it. Just surprised me that it still worked without a map.
Thanks for clearing it up!
Cheers
On Tuesday, September 15, 2015 at 10:29:08 PM UTC-6, Carlo wrote:
>
> Symbols and keywords act as functions which look themselves up in their
> argument. Essentially:
>
> ('sym map) => (get map 'sym)
> ('sym map not-found) => (get map 'sym not-found)
>
> (:key map) => (get map :key)
> (:key map not-found) => (get map :key not-found)
>
> It's often pretty useful, in my experience. It looks cleaner, and it
> means that you can just use :keyword instead of #(get % :keyword) in
> cases where you provide a function as an argument (for example: (map
> :type objects)).
>
> On 16 September 2015 at 14:20, Michael O'Keefe <[email protected]
> <javascript:>> wrote:
>
>> Hello All:
>>
>> Noticed the following works in Clojure 1.6 and 1.7 (didn't test prior to
>> that):
>>
>> user=> ('+ 'a 'b)
>> b
>>
>> Also "works" for any set of symbols:
>>
>> user=> ('abra 'ka 'dabra)
>> dabra
>>
>> My expectation was that using symbols or keywords in the
>> function/operator position would throw an exception similar to this:
>>
>> user=> (3 4)
>>
>>
>> ClassCastException java.lang.Long cannot be cast to clojure.lang.IFn
>> user/eval7668 (form-init2947310628177413729.clj:1)
>>
>>
>> I noticed Keywords can also be used in the operator position:
>>
>> user=> (:abra :ka :dabra)
>> :dabra
>>
>> And mixing and matching is OK:
>>
>> user=> (:a 'b 3)
>> 3
>>
>> It seems to act something like an implicit `do` in that it returns the
>> last value but, in fact, not quite as you seem to need to have more than
>> two items:
>>
>> user=> ('do)
>>
>> ArityException Wrong number of args (0) passed to: Symbol
>> clojure.lang.AFn.throwArity (AFn.java:429)
>>
>>
>> user=> ('do (+ 1 2 3))
>> nil
>>
>>
>> user=> ('do 'this (+ 1 2 3))
>> 6
>>
>> But more than 3 is not accepted:
>>
>> user=> ('do 'this 'please 3)
>>
>>
>> ArityException Wrong number of args (3) passed to: Symbol
>> clojure.lang.AFn.throwArity (AFn.java:429)
>>
>> user=> ('do 'this 'please 'now 'ok?)
>>
>>
>> ArityException Wrong number of args (4) passed to: Symbol
>> clojure.lang.AFn.throwArity (AFn.java:429)
>>
>>
>> A quick search didn't reveal any bug reports or previous discussions on
>> this but I may have missed something (feel free to point me in the right
>> direction).
>>
>> Is it just a "quirk" or is it useful in some way? Intended behavior or
>> bug?
>>
>> Cheers,
>>
>> Michael O'Keefe
>>
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>
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