Metadata on symbols differ with caret reader
mdzaebel
(meta ^:k []) --> {:tag :k}
(meta ^:k 'o) --> nil
(meta(with-meta 'o {:tag :k})) --> {:tag :v}
Why doesn't the second line return the metadata?
Thanks, Marc
Using Clj 1.2
Meikel Brandmeyer
Am 09.01.2011 um 22:52 schrieb mdzaebel:
> (meta ^:k []) --> {:tag :k}
> (meta ^:k 'o) --> nil
> (meta(with-meta 'o {:tag :k})) --> {:tag :v}
>
> Why doesn't the second line return the metadata?
Because 'o expands to (quote o) and you actually hint this list. You might try (meta ' ^:k o).
Sincerely
Meikel
Tim Robinson
In line 1 (meta ^:k []) does not return {:tag :k} it returns nil and
I am using Clojure 1.2.
Both lines 1 and 2, shouldn't return meta, because 'meta' only takes
an object as an input argument.
And only if the object already has metadata will metadata will return.
=> (def o (with-meta ['mydatastructure] {:k []}))
=> (meta o)
{:k []}
Meikel Brandmeyer
Am 10.01.2011 um 01:10 schrieb Tim Robinson:
> You must have something messed up:
>
> In line 1 (meta ^:k []) does not return {:tag :k} it returns nil and
> I am using Clojure 1.2.
>
> Both lines 1 and 2, shouldn't return meta, because 'meta' only takes
> an object as an input argument.
> And only if the object already has metadata will metadata will return.
>
> => (def o (with-meta ['mydatastructure] {:k []}))
> => (meta o)
> {:k []}
Are you sure?
Clojure 1.2.0
user=> (meta '^:k o)
{:tag :k}
user=> (meta ^:k [])
{:tag :k}
user=> (meta (with-meta 'o {:tag :k}))
{:tag :k}
user=> (meta ^:k 'o)
nil
The ^ stuff all works in the reader. So meta always sees only one argument with metadata already attached. The question is: Where is the meta data attached?
Sincerely
Meikel
Tim Robinson
But I am using 1.2 and when I run (meta ^:k []) or even (meta '^:k o)
I get nil.
Plus:
app=> (doc meta)
-------------------------
clojure.core/meta
([obj])
Returns the metadata of obj, returns nil if there is no metadata.
nil
I could be missing something?
Tim Robinson
{:tag :k}
If you launch a brand new repl and run it what happens?
Meikel Brandmeyer
On 10 Jan., 04:17, Tim Robinson <tim.blacks...@gmail.com> wrote:
> How does this happen when :tag is not even in the expression?
> If you launch a brand new repl and run it what happens?
and what happens there with 1.2. And in fact, that it is what I would
expect.
^String is a short-hand notation for ^{:tag String}. There was a
change planned for using ^ with keywords, namely that ^:foo is short-
hand for ^{:foo true}. But I don't know whether this change made it
into 1.3.
Sincerely
Meikel
mdzaebel
On 10 Jan., 01:09, Meikel Brandmeyer <m...@kotka.de> wrote:
> Because 'o expands to (quote o) and you actually hint this list. You might try (meta ' ^:k o).
my books or the reader section of clojure.org mentioned it.
Thanks a lot, Marc
Tim Robinson
My downloaded version of clojure 1.2.0 acts exactly as you describe.
However my basic lein project with only
(defproject prj "1.0.0-SNAPSHOT"
:dependencies [[org.clojure/clojure "1.2.0"]]])
acts differently.
Well as I said, I can never sure about anything :)
Cheers
Tim
Meikel Brandmeyer
On 10 Jan., 14:36, Tim Robinson <tim.blacks...@gmail.com> wrote:
> Interesting.
Suspicious, I'd say.
> My downloaded version of clojure 1.2.0 acts exactly as you describe.
>
> However my basic lein project with only
>
> (defproject prj "1.0.0-SNAPSHOT"
> :dependencies [[org.clojure/clojure "1.2.0"]]])
>
> acts differently.
> Well as I said, I can never sure about anything :)
Sincerely
Meikel
Stefan Kamphausen
I can't verify that a REPL created by lein behaves differently. Did you perhaps update an old project.el without running lein deps?
In addition to that: your defproject has too many ]'s
Regards,
Stefan
Tim Robinson
:)