Ah!
Thanks to all.
Yes, I was a bit confused, thinking ^ expands as ' (quote), to use
(with-meta..). But there is not expansion. It really applies the map to the
next read form, expecting the read form implements IObj:
public interface IObj extends IMeta {
public IObj withMeta(IPersistentMap meta);
}
So. ^{ .... } applied to a symbol, returns a new symbol. From Symbol.java:
public IObj withMeta(IPersistentMap meta){
return new Symbol(meta, ns, name);
}
I have seen the light! ;-)
Time to refactor my code, TDD will save my day
Angel "Java" Lopez
@ajlopez
On Sat, May 3, 2014 at 6:51 PM, Stephen Gilardi <[email protected]> wrote:
> 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?
>
>
> The description above is literally how it works: "The metadata reader
> macro first reads the metadata and attaches it to the next form read”.
>
> Reader macros are implemented within the reader. They are distinct from
> defmacro macros.
>
> The implementation is here:
>
> https://github.com/clojure/clojure/blob/clojure-1.6.0/src/jvm/clojure/lang/LispReader.java#L706
>
> The reader reads from an input stream; it:
>
> - reads the metadata object, meta [L716]
> - reads the object that follows it, o [L724]
> - figures out how to apply meta to o based on the interface(s) o
> implements [L725.L731]
> - applies meta to o [L733,L741]
>
> —Steve
>
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