[Openmcl-devel] How abour top-level setf = REPL-lexical variables? (was Re: Compiler warnings)
kpreid at mac.com
Tue Oct 20 02:00:27 UTC 2009
On Oct 19, 2009, at 21:34, Ron Garret wrote:
[in a long thread about the behavior of top-level setf]
> Yes. I'm doing some testing, so I want some place to stash an
> intermediate result. I do:
> (setf x ...)
> Later, after I'm long done with that and the fact that I once created
> a global variable named X, I do this:
> (defun make-closure (x) (lambda () ... x ...))
> I then expect MAKE-CLOSURE to return a lexical closure.
IMO, the best way to make this DWIM (which as far as I know is
conformant (in that the REPL is mostly unspecified) but not currently
done by any CL implementation) is to make x a *lexical* variable which
is managed by the REPL. Your example would then do exactly what you
That is, when you evaluate the expressions in the REPL it behaves *as
if* every free variable is a lexical variable established by an
enclosing LET. (This particular semantic explanation gets weird if
you do, say, (list x (setf x 1)), but this doesn't seem to me to be a
large problem whether it is rejected or just returns (NIL 1).)
There could also be functions to display the current set of REPL
variables and delete them.
I think this facility would have the following benefits:
- Saves typing when playing around at the REPL, since there's no need
for *special* markers.
- Reminds you what you created as an interactive temporary vs. what
global state of the application, both syntactically and because you
can get a list of them.
- Fits what a lot of beginners expect, because they're
- coming from Perl/Python/PHP/whatever
- using ancient tutorials/samples with top-level setq/setf
(This isn't just a beginner thing -- *I* would greatly like to have
this feature to save me inventing special-variable names while
And it's AFAIK fully conformant with CLHS.
Kevin Reid <http://switchb.org/kpreid/>
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