On Dec 5, 2:10 pm, Alex Ott <alex...@gmail.com> wrote:
> Re
>
> jweiss at "Sun, 5 Dec 2010 10:29:41 -0800 (PST)" wrote:
> j> I'm no expert on this, but i'll take a crack at it.
>
> j> I think it's because sets don't (necessarily) impose any order, so
> j> there's no concept of "first" or "nth". So destructuring would
> j> essentially be assigning a random item to x, or for join, joining them
> j> in random order.
>
> Sometimes, order doesn't matter, for example, I want to print data from set
> (or any collection that is transformable into sequence), using some
> separator between elements...
>
> For some operations we can't also predict order, for example, conj behaves
> differently for lists and vectors
>
> --
> With best wishes, Alex Ott, MBAhttp://alexott.blogspot.com/
> http://alexott.net/http://alexott-ru.blogspot.com/
> Skype: alex.ott
If you wanted to, for example, print a set with separators in between,
would you need to use destructuring?
I'd just do (apply str (interpose "," #{:a :b :c})
-> ":a,:b,:c"
I don't think conj adding to the front for lists and the end for
vectors is unpredictable at all. I know that
(conj '(1 2) 3))
-> (3 1 2)
and
(conj [1 2] 3)
-> [1 2 3]
before I even type it on a REPL. That's totally different than nth
for a set being undefined. It's undefined on purpose.
Now, if you are using a sorted-set, then you have a point there, I
would expect that nth means something then. But yeah, clojure doesn't
let you call nth on it directly, you have to make a seq out of it
first. Not sure what the performance implication is there, but it's
not much effort to write:
(nth (sequence (sorted-set 1 3 2)) 2)
-> 3
I will let people who are more knowledgeable comment on why there's no
nth on a sorted-set.
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