Re: [Scheme-reports] What happened to (UNQUOTE <expression> ...)

[Peter Bex <Peter.Bex@x>]

On Sat, Apr 23, 2011 at 11:09:34PM -0400, Andre van Tonder wrote:
> > It looks reasonable to me, but could you point us
> > to the discussions or rationales?
> >
> > Specifically, how is (unquote-splicing a b c) different from
> > ,@a ,@b ,@c ?
> 
> I think the issue is a little more complex that this, it has to do with the 
> fact that nested unquote-splicing was accidentally broken in Scheme, but since I 
> don't remember the details offhand, let me quote Al* Petrofsky on this issue. 

Thank you for this rationale.  I asked about the same issue before, but
that part of my message was ignored.  I considered the R6RS change rather
unintuitive, but the case of unquoting to undo nested quoting levels for
one spliced unquote makes sense.

If this makes it into R7, I would like to see a rationale for this added.
I looked for one in R6 and couldn't find it in there.  I think this is
necessary considering this is very strange behaviour: I compared it to
implicit splicing of MV into the calling expression.  It still feels like
that to me, but at least now I understand why it's necessary or useful.

PS: Andre, could you please consider not replying to an earlier message
when posting a new, unrelated issue?  This confuses mailclients with
threading support because the in-reply-to header contains the message ID
of the message you're replying to; this causes my mailclient to think all
your messages of today belong to one giant thread :(

It also messes up the archive's threaded view at
http://lists.scheme-reports.org/pipermail/scheme-reports/2011-April/thread.html
but the mailman software is broken in another way.

Cheers,
Peter
-- 
http://sjamaan.ath.cx
--
"The process of preparing programs for a digital computer
 is especially attractive, not only because it can be economically
 and scientifically rewarding, but also because it can be an aesthetic
 experience much like composing poetry or music."
							-- Donald Knuth

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