WEBVTT captioned by sachac and robin
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Hello everyone. I'm Robin Templeton, and I'm going to talk
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about Emacs Beguiled and recent progress on the Guile-Emacs
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project.
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First of all, if you're not familiar with Guile, it's an
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implementation of the Scheme programming language, which
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is a dialect of Lisp, and in the same family as Emacs Lisp, and
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Guile is GNU's official extension language. The goal of
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the Guile-Emacs project is to use Guile as the basis for
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Emacs's Lisp support. It has two main components: a new
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Emacs Lisp compiler built on top of Guile, and a variant of
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Emacs in which the built-in Lisp implementation is
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entirely replaced with Guile Elisp. We expect the
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combination of these two projects to have several
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benefits. One is improved performance. Another is
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increased expressiveness for Elisp and making it easier to
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extend and experiment with the language. Finally, it
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will reduce Emacs's reliance on C for two reasons. Guile will
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be responsible for the language implementation, so Emacs
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will no longer have to include a Lisp interpreter. It
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will also become possible to implement much more of Emacs in
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Lisp than is currently feasible. Of course, this raises
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the question of why Guile is suitable for this project. And
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we chose Guile for a few reasons. Guile is primarily a Scheme
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implementation, but it also has built-in support for
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multiple languages using its compiler tower. To add
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support for a new language to Guile, you only have to write a
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compiler from the source language to Tree-IL, which is
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essentially a low-level, minimal representation of
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Scheme. All of Guile's compiler optimizations occur at the
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Tree-IL layer or lower, so you don't need to worry about the
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lower-level details of the compiler when initially
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implementing your language. Guile also has some Lisp
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features that are very rare in Scheme implementations. For
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example, it has a nil value that counts as both false and an
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empty list, just like in Elisp, and it also has a version of
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the Common Lisp Object System and its metaobject protocol,
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which is called GOOPS.
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The idea of Guile-Emacs has a pretty long history, going back
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at least three decades. There have been about half a dozen
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previous implementation attempts. But the current
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iteration began with a series of six Summer of Code
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internships: Daniel Kraft's in 2009, and then my
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internships from 2010 to 2014. My basic implementation
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strategy was pretty straightforward. I implemented a core
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subset of Elisp, which was enough to run some batch mode
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programs outside of Emacs. In Emacs, I modified the garbage
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collector and the data structures for Lisp objects to use
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their libguile equivalents. I replaced Emacs' Lisp
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evaluator with the one provided by Guile Elisp.
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After a little over a year of work, at the end of the 2014
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internship, I ended up with a fully functional prototype of
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Guile-Emacs. It used Guile Elisp alone as its Lisp
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implementation and was completely compatible with Emacs
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functionality and with external extensions. One caveat
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was that performance was pretty bad, because I was focused
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on correctness, as well as ease of integration with the
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Emacs C code. But it was nonetheless a major milestone for
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the project. Let's take just a moment to look at
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Guile-Elisp.
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For starters, we have access to Guile modules. If we call
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Guile's <i>version</i> function, we can see that we're running
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under Guile 3.0. We have access to some of the numeric tower via
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the arithmetic functions. We also have multiple values. We
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have to be careful to use Guile's <i>values</i> procedure here, not
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the CL library's, but you can see that this works properly
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rather than being an emulation. Finally, we have tail
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call elimination. Naturally, we're going to use factorial
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to demonstrate it. If <i>n</i> is zero, return the answer, else
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recurse with <i>n</i> less one and <i>n</i> times <i>a</i>.
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Of course, this definition works correctly, but it gets
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more interesting if we communicate the answer with an
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error,
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in order to look at a backtrace. You can see here that there are no
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calls to <i>fact</i> visible in between the request to evaluate and
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the error communicating the answer. That's because
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this tail call has been optimized into effectively a goto.
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This is essential for any kind of serious functional
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programming.
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That's a peek at Guile-Elisp. In 2015, I left university
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to go work on web technologies, and the project was dormant
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for a very long time. But that's been changing recently.
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During the last few months, I've been working with Larry
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Valkama to rebase Guile-Emacs onto the development branch
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of upstream Emacs, including the past decade's worth of
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upstream development. What we've ended up with is a series
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of rebases onto different versions of Emacs. The older ones
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tend to work pretty well. The newer ones have increasingly
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bad problems where they haven't been properly adjusted for
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changes in the Emacs implementation. But we do have by now a
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version of Emacs 30 which boots correctly and can be used for
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interactive debugging, as well as the ability to bisect the
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revisions of Emacs and find out where regressions were
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introduced. Our immediate goal is of course to complete
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the rebase. At the same time, we want to improve Guile Elisp's
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performance to at least be competitive with ordinary Emacs
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Lisp. Just to characterize the performance situation,
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Guile Elisp is usually about half as fast as ordinary Elisp,
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while Guile Scheme is quite often an order of magnitude
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faster than ordinary Elisp, and that's based on micro
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benchmarks like the Gabriel benchmarks. But there's
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clearly a lot of room to improve our compiler's output.
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If you want to mark your calendars, we're expecting to have a
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usable version of Guile-Emacs 30 out sometime next spring. We're
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also going to put some effort into either extracting old
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work or doing new work that could be contributed upstream.
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On the Guile side, we'll probably start out with optimizing
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the dynamic binding facilities, which are used very seldom
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in Scheme, but are used all the time in traditional Lisp
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dialects. On the Emacs side, we'll be working initially on
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abstracting away the details of the Lisp implementation
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where they're not relevant. And that will clean up the Emacs
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code base a bit. It'll make it easier to integrate Emacs and
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Guile Elisp. It will probably be helpful for anyone who
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is working on ordinary Elisp on their own.
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We're also going to be adding new features to Emacs Lisp.
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We've seen a few of them already. The numeric tower, tail
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call optimization, Common Lisp compatibility. We're also
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going to provide access to Fibers, which is a Guile library
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based on ideas from Concurrent ML that provides much more
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powerful facilities for concurrent and parallel
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programming than what Emacs currently offers.
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This plan meets Guile-Emacs' basic goals, and it's work
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that we could maybe get integrated upstream in a reasonable
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amount of time. But it's also worth considering what more we
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can do, and what effect Guile-Emacs might have on Emacs if it
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becomes simply Emacs.
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For context, the amount of C code in Emacs has increased by
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around 50% in the last decade, and now it constitutes around
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a quarter of the code base. C can be a bit of a barrier to
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customizing and extending Emacs. For example, there are
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about 1500 C subroutines. Around 500 are used in C code, as
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well as available to Lisp code, and being written in C means
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that they can't be practically redefined. The use of C can
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become a barrier to extending Emacs or customizing its
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behavior. We might consider writing as much of Emacs as
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possible in Lisp. One way to speed up this process would
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be to provide a Common Lisp implementation for Guile. Note
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that between Guile Elisp and Guile Scheme, we have all of
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the essential ingredients for a Common Lisp environment.
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We can also share code with other Common Lisp
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implementations such as SBCL and SICL. Overall, the
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duration of the project will be better measured in months
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rather than years, despite Common Lisp's reputation for
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being a large language. This could have multiple uses, of
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course. It could be a model for future improvements to
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Elisp, because Elisp and CL can interact directly without
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problems. And it would be very easy for Elisp to borrow
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language features from Common Lisp. But for the purpose of a
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C to Lisp transition, it would also provide us with instant
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access to a huge number of high-quality libraries for
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things that Guile is not necessarily equipped to deal with,
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such as access to low-level Windows APIs, as well as lots of
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other libraries, such as interfaces to GUI toolkits for a
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variety of operating systems.
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At a certain point, this has technical advantages. If
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most of Emacs is written in Lisp, then we could consider
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using Guile Hoot to compile Emacs to WebAssembly, making it
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available perhaps in web browsers or on systems with the
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WebAssembly System Interface. But it would also be a great
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victory for practical software freedom. That's the idea
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that Freedom One, the freedom to study and modify programs,
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should not just be legally and technically possible, but
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should be actively encouraged by our computing
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environments. Emacs is really one of the archetypal
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examples of this, but we can and should go further.
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When Emacs is implemented primarily in Lisp, the entirety
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of the system will be transparent to examination and open to
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modification. Every part of Emacs will be instantaneously
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inspectable, redefinable, and debuggable.
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This will be a fundamental change in what is possible to
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do with Emacs extensions. For example, one experiment I'd
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be interested in is using the Common Lisp Interface Manager
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as the basis for Emacs's user interface. Screwlisp is
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giving a talk about McCLIM later today, but for present
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purposes, just think of it as a super-powered version of
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Emacs's concept of interactive functions. It would be a
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pretty long-term project in Emacs as it currently exists,
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but it would be almost trivial if Emacs were customizable at
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the lowest layers via Lisp.
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We'll certainly be looking at the practicality of these
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kinds of changes as we continue developing Guile-Emacs.
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Finally, how can you get involved with and support Guile
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Emacs? One way to help is just by trying it out and letting us
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know what your experiences are like. There will be a
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snapshot available on the Codeberg project site of the
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version that I'm using to give this presentation. It will be
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available both as a Guix package and as a portable tarball.
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This will be more interesting as we get closer to a complete
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rebase. We're also always happy to talk to potential
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contributors or potential collaborators from other
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projects.
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We can always use bug reports, and we're interested in what
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kind of features people actually want to see in Guile-Emacs.
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Guile-Emacs is also being developed by a small worker
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cooperative, so donations are a pretty direct way to
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support the project. If you do nothing else, I recommend
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going to the website and subscribing to our mailing lists so
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that you can keep up with news on the project. If you're
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watching this at EmacsConf, there will be a Q&A session
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immediately following this, and thanks for watching!
