Re: Unexpected behavior for symbols or keywords used in the operator position
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 > 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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Unexpected behavior for symbols or keywords used in the operator position
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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Re: Unexpected behavior for symbols or keywords used in the operator position
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
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
>
> --
> You received this message because you are subscribed to the Google
> Groups "Clojure" group.
> To post to this group, send email to clojure@googlegroups.com
> Note that posts from new members are moderated - please be patient with
> your first post.
> To unsubscribe from this group, send email to
> clojure+unsubscr...@googlegroups.com
> For more options, visit this group at
> http://groups.google.com/group/clojure?hl=en
> ---
> You received this message because you are subscribed to the Google Groups
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> To unsubscribe from this group and stop receiving emails from it, send an
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> For more options, visit https://groups.google.com/d/optout.
>
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