On Feb 23, 4:21 am, Christophe Grand <christo...@cgrand.net> wrote:
> Chouser a écrit :
>
>
>
> > On Sun, Feb 22, 2009 at 4:07 PM, jim <jim.d...@gmail.com> wrote:
>
> >> In some old code, I did something like:
>
> >> (with-meta (concat [1 3] [8 4])
> >> {:tail true}))
>
> >> which now fails. I believe it's because the result of concat is now
> >> some kind of reference.
>
> >> Does anyone have any advice on a workaround?
>
> > LazySeq extends AFn, so you can't change the metadata once the object
> > exists. However, Seq's still accept meta-data, so:
>
> > (with-meta (seq (concat [1 3] [8 4]))
> > {:tail true})
>
> I'm not sure it's desirable to have metadata on seqs (it bit me while
> transitionning to lazy) but I have thought of two ways to add withMeta
> to a LazySeq:
> * to have meta()/withMeta() to force evaluation of the inner seq (and it
> begs the question to know whether (= (meta a) (meta (lazy-seq a)))
> should be true),
> * to have withMeta() to return some kind proxy on the LazySeq object
> (cannot this approach also works for regular closures?).
>
> BTW, speaking of regular closures, would it be possible to be able to
> set "static" metadata?
> eg:
> (#^{:meta {:actual :metadata}} fn* [args] body)
>
> (The fn macro could make this prettier.)
>
The fact that LazySeqs are AFns is an implementation detail that might
change. I still have some perf tweaking to do. After that, we can look
at how best to support metadata.
Rich
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