... the other half of the answer being that when you have rest args with
(defn foo [& args] ...), "args" is bound to a seq.
On Wed, Aug 27, 2014 at 11:27 AM, Ben Wolfson <wolf...@gmail.com> wrote:
> The reason is that in the macroexpansion of "let", map-based destructuring
> has a seq? test which the list passes but the vector doesn't:
>
> > (clojure.pprint/pprint (macroexpand-1 '(let [{:keys [a b]} [:a 1]] a)))
> (let*
> [map__34214
> [:a 1]
> map__34214
> (if
> (clojure.core/seq? map__34214)
> (clojure.lang.PersistentHashMap/create
> (clojure.core/seq map__34214))
> map__34214)
> b
> (clojure.core/get map__34214 :b)
> a
> (clojure.core/get map__34214 :a)]
> a)
>
> Presumably this is because vectors can also be accessed with "get", so you
> can do something like this:
>
> > (let [{a 0} [:a 1]] a)
> :a
>
> ... confusing though it is.
>
>
>
> On Wed, Aug 27, 2014 at 11:20 AM, John Gabriele <jmg3...@gmail.com> wrote:
>
>> Why is it that although this works:
>>
>> ~~~clojure
>> (defn foo [& args] (let [{:keys [a b]} args] (str a \~ b)))
>> ;;=> #'some-app.core/foo
>> (foo :a 1 :b 2)
>> ;;=> "1~2"
>> ~~~
>>
>> this does not:
>>
>> ~~~clojure
>> (let [{:keys [a b]} [:a 1 :b 2 :c 3]] (str a \~ b))
>> ;;=> "~"
>> ~~~
>>
>> ?
>>
>> And even stranger, *this* *does* work:
>>
>> ~~~clojure
>> ;; Changed vector to a list.
>> (let [{:keys [a b]} '(:a 1 :b 2 :c 3)] (str a \~ b))
>> ;;=> "1~2"
>> ~~~
>>
>> ?
>>
>> Incidentally, I see that the following `let` also does indeed work:
>>
>> ~~~clojure
>> (let [ [& {:keys [a b]}] [:a 1 :b 2 :c 3] ] (str a \~ b))
>> ;;=> "1~2"
>> ~~~
>>
>> Thanks!
>>
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>
>
>
> --
> Ben Wolfson
> "Human kind has used its intelligence to vary the flavour of drinks, which
> may be sweet, aromatic, fermented or spirit-based. ... Family and social
> life also offer numerous other occasions to consume drinks for pleasure."
> [Larousse, "Drink" entry]
>
>
--
Ben Wolfson
"Human kind has used its intelligence to vary the flavour of drinks, which
may be sweet, aromatic, fermented or spirit-based. ... Family and social
life also offer numerous other occasions to consume drinks for pleasure."
[Larousse, "Drink" entry]
--
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