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!
>
> --
> 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
> "Clojure" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to clojure+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
>
--
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]
--
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
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
