The evaluation of meta data happens when the def form is evaluated:
user=> (meta (second (read-string "(def ^{:key (+ 1 1)} foo)")))
{:key (+ 1 1)}
vis a vis
user=> (meta (eval (read-string "(def ^{:key (+ 1 1)} foo)")))
{:ns #<Namespace user>, :name foo, :file "NO_SOURCE_PATH", :line 1, :key 2}
The reader doesn't interact with the runtime, except for resolving the
current namespace in backtick `forms and and for reader tags and related
mechanisms.
A little experiment in clojure 1.5.1 showed, that during AOT compilation,
the meta data gets evaluated twice, but it is still evaluated when
require'ing the resulting class files.
2013/3/19 Angel Java Lopez <ajlopez2...@gmail.com>
> Thanks Jean!
>
> Yes, I did that test before my email.
>
> But my doubt is:
>
> What part is in charge of metadata evaluation?
>
> From such test, I can't deduce if the metadata evaluation is made by the
> reader, or by the macro def.
>
> If the metadata evaluation is made by the reader, the symbol two will have
> {:a 2} as metadata, and then, the macro def get the metadata from the
> symbol and assign the var the def macro is defining.
>
> But the online docs maybe describe other way:
>
> "Any metadata on the symbol will be evaluated, and become metadata on the
> var itself."
>
> That is, the metadata ALREADY in symbol, is then EVALUATED by def special
> form.
>
> My context: I'm writing an interpreter of Clojure, in C#, to practice TDD,
> with behavior based on published doc, or core.clj, I'm not sure what is the
> expected behavior of the reader, metadata and special form.
>
> Maybe, the two options I described in my first email, are EQUIVALENT for
> all practical purpose, but I have the doubt, and I don't know how to write
> a clojure code that helps me to discover the current behavior
>
> Angel "Java" Lopez
> @ajlopez
>
> On Tue, Mar 19, 2013 at 7:35 AM, Jean Niklas L'orange <
> jeann...@hypirion.com> wrote:
>
>>
>>
>> On Tuesday, March 19, 2013 9:49:09 AM UTC+1, ajlopez wrote:
>>>
>>> Hi everyone!
>>
>>
>> Hi!
>>
>> The easiest thing to find out of this would be to check it out:
>>
>> (def ^{:a (+ 1 1)} two 2)
>> ;=> user/two
>> (meta #'two)
>> ;=> {.... :a 2}
>>
>> So indeed, the forms within metadata is evaluated.
>>
>> -- Jean Niklas L'orange
>>
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