I'm trying to implement in my clojure interpreter (in c#) the metadata
reader. I read in core.clj something like
(ns ^{:doc "The core Clojure language."
:author "Rich Hickey"}
clojure.core)
I just read:
http://clojure.org/reader
- Metadata (^)
Metadata is a map associated with some kinds of objects: Symbols, Lists,
Vector, Sets, Maps, tagged literals returning an IMeta, and record, type,
and constructor calls. The metadata reader macro first reads the metadata
and attaches it to the next form read (see
with-meta<http://clojure.github.io/clojure/clojure.core-api.html#clojure.core/with-meta>
to
attach meta to an object):
^{:a 1 :b 2} [1 2 3] yields the vector [1 2 3] with a metadata map of
{:a 1 :b 2}.
Ok, but how the reader works?
I tried
(def one 1)
^:foo one
and it works
But i tried
^:foo bar
and it yields an error (Unable to resolve the symbol bar...)
But then
(ns ^:foo bar)
IT WORKS!
Where the attached form to metadata is evaluated?
I thought that
^:foo bar
was expanded as
(with-meta bar {:foo true})
in the same way like
'a
is expanded to
(quote a)
and then (with-meta bar {:foo true}) is passed to ns.
I know that ns is a macro. So the attachment of the metadata is not yet
evaluated. But when it is evaluated? Is it true that ns receives (with-meta
bar {:foo true})? Or in which way the ^ reader works?
I checked ns source
https://github.com/clojure/clojure/blob/028af0e0b271aa558ea44780e5d951f4932c7842/src/clj/clojure/core.clj#L5304but
apparently it is some magic detecting the metadata
Any clue?
Angel "Java" Lopez
@ajlopez
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