Content tagged lisp

Big Changes for Coleslaw
posted on 2014-09-22 10:36:00

I'm working towards 1.0 and Coleslaw's basic architecture seems to have settled down. The areas of focus for 1.0 will be better error handling, command-line conveniences, more content types, and possibly some new ways to ingest data.

Coleslaw 0.9.6 will be released this Saturday and, not long after, make it into the next quicklisp release. Seeing as it contains big changes, some of them breaking, I thought I'd put out an announcement.

Coleslaw 0.9.6

Coleslaw 0.9.6 unifies how we handles URLs throughout the application and simplifies the deploy strategy. The good news is, this makes the install process easier for new users. The bad news is, if you've got an existing install, you'll need to add a new plugin (versioned) to your config file for the old deploy behavior.

That's not so rough, right? In addition, custom themes and plugins that haven't been upstreamed may need some minor tweaks. The NEWS has more details.

Feel free to grab the basic-deploy branch from my repo and try it out. There are some new docs and the README has been cleaned up. There's also a plugin for Twitter Summary Card support and the usual smattering of bugfixes.

Going Forward

While I'm happy to maintain Coleslaw if no one else steps up to work on it, I'm going to try and shift my focus towards emulation work and weird lisp noodling. If you're interested in taking on a co-maintainer role or working with me on the project please get in touch. I've been very appreciative of the help and interest thus far. If there's anything I can do to make the project more approachable or help people get started, do let me know.

Breaking Radio Silence
posted on 2014-05-05 13:12:11

Long time, no blog.

I've been offline for a while. I burned out last July and only really started hacking on my lisp projects again in March. So what's changed in the last two months? Actually, kind of a lot.

Coleslaw 0.9.4

Coleslaw 0.9.4 is hereby released. I apologize that 0.9.3 which went out in the last quicklisp release had an embarrassing escaping bug.

The most fun part of Coleslaw is trying my hand at API design. Lisp is a great tool for writing extensible software and Coleslaw has been a good proving ground for that since everyone has a slightly different set of requirements for their blogware.

I've been reading Sonya Keene's Object Oriented Programming in CL lately which led to a large refactoring around the new Document Protocol. I'm not prepared to say anything intelligent about protocols yet, but thankfully plenty of people have done so elsewhere. This blog post by sykopomp isn't a bad place to start.

In addition to the document protocol and the usual litany of bugfixes, Coleslaw now has a new theme based on bootswatch readable, user-defined routing, support for static pages, and greatly expanded docs.

The main things to tackle before 1.0 are a plugin to support incremental compilation for very large sites and a twitter/tumblr cross-posting plugin.

cl-6502 0.9.7

Additionally, someone actually found a use for my Readable CPU emulator! Dustin Long was working on a homebrew Nintendo game and wanted a way to unit test his code, so he's been using cl-6502 to get cycle counts and otherwise check behavior. Naturally, the very basic assembler got on his nerves so he sent me a nice pull request adding support for labels, compile-time expressions, and decimal, hex, and binary literals. Thanks, Dustin!

I also rewrote the addressing modes again, reduced consing, and made debugging easier by using Alexandria's named-lambda for all the opcodes. The cl-6502 book has been updated, of course.


With any luck, I'll get back to work on famiclom or tools for analyzing old NES games like Super Mario Bros and Mega Man 2. It's good to be back.

Lessons from cl-6502
posted on 2013-07-05 11:44:00

This will be the last post about emulation that doesn't involve graphics or disassembly of old NES games, I promise. cl-6502 0.9.5 is out and, in my testing with SBCL, pretty snappy. The book has received updates and is also available on lulu. Below is the 'Lessons Learned - Common Lisp' chapter:

Structures can be preferable to classes

Structures are much more static than classes. They also enforce their slot types. When you have a solid idea of the layout of your data and really need speed, they're ideal.

CLOS is fast enough

CLOS, for single-dispatch at least, is really quite fast. When I redesigned the emulator to avoid a method call for every memory read/write, my benchmark only ran ~10% faster. I eventually chose to stick with the new scheme for several reasons, performance was only a minor factor.

Destructuring is more expensive than you think

My second big speedup came, indirectly, from changing the arguments to the opcode lambdas. By having the opcode only take a single argument, the CPU, I avoided the need to destructure the opcode metadata in step-cpu. You don't want to destructure a list in your inner loop, no matter how readable it is!

Eval-when is about data more than code

That is, the times I found myself using it always involved computing data at compile-time that would be stored or accessed in a later phase. E.g. I used it to ensure that the status-bit enum was created for use by set-flags-if and the *mode-bodies* variable was bound in time for defaddress. Regardless, try to go without it if possible.

Use DECLAIM (and DECLARE) wisely

DECLAIM is for global declarations and DECLARE is for local ones. Once you've eked out as many algorithmic gains as possible and figured out your hotspots with the profiler, recompile your code with (declaim (optimize speed)) to see what is keeping the compiler from generating fast code. Letting the compiler know the FTYPE of your most called functions and inlining a few things can make a big difference.

My Lisp Summer Project
posted on 2013-06-21 14:58:00

cl-6502 0.9.4

I haven't been doing any hacking on coleslaw or famiclom for the last month. I've been focused almost entirely on my 6502 CPU emulator. In particular, I've been optimizing it and turning it into a "readable program".

The optimizations have gone swimmingly, taking cl-6502 from 3.8 emulated mhz circa May 1st (commit eecfe7) to 29.3 emulated mhz today (commit b729e8).(0) A factor of 8 speedup feels pretty good though it would be fun to coax more speed out later.

(0): All figures obtained with SBCL 1.1.4 on Debian 64-bit on an old Thinkpad X200. See this 6502 forum post.

I feel that the readability of the program has remained, maybe even improved, through all that optimization. The same overall design is in place; most refactorings were, approximately, tweaking macros and their callsites. The readability is especially improved when the code is broken into chapters, each with an introduction for context, and typeset with LaTeX. The latter is done thanks to a simple Makefile and some very nifty code swiped from Luke Gorrie's snabbswitch. If you've been curious about how cl-6502 is implemented or just wanted to dive in, there's never been a better time. Grab the book!

NES + Lisp + Static Analysis = ?

I'm still planning to make famiclom a full NES emulator. I won't consider it done until I can play Mega Man 2 with it. Hopefully using a USB controller. It doesn't make much sense for Lisp in Summer Projects though. I've already started the project, the scope is ill-defined, and I want to work on something fresh and new to me. So I've come up with a project that I can't possibly complete instead. It'll be great!

In short, I intend to rewrite Super Mario Bros 1. ... in a not-yet-existing lisp-like macro-assembler/incredibly simple compiler. I already have a 6502 assembler/disassembler in cl-6502 and a tool to parse NES roms in romreader. There's also a very thorough annotated disassembly of Super Mario Bros floating around. I've got a good start on a static analyzer that will take the SMB binary and an entry point and try to build a CFG of the game. The current scheme won't work with memory mapped titles but it's good enough for Mario.

Wild Speculation

Once I have a graph representation of Mario Bros, I'll try both manual analysis of the annotated disassembly with a pen and pad, and automated analysis on the graph using Lisp. I'll try to find as many idioms and patterns as possible to condense and improve readability of the code. Then, somewhere in early August, I'll start trying to rewrite the source and see how far I can get.

This approach is probably completely: insane, unworkable, unviable, inadvisable, and just all around wrong. But I think I'll have fun and learn something, so it's good enough for me. And hell, who knows, maybe I'll get lucky and be able to attend ECLM next year. :)

Coleslaw 0.9.2 and other lispiness
posted on 2013-05-11 20:41:00

Coleslaw 0.9.2

It still amuses me that my most successful project to date is a blog engine. Not that I'm complaining about having contributors. When I last mentioned it, version 0.8 had just been released. Since then there have been 2 new contributors and a bunch of new features. I think the code has mostly improved in cleanliness.

The biggest changes are new shiny docs, a new tags implementation, cleanups to theming, and plugins for Google Analytics, Github Pages, and Sitemap Generation. For the full details, see the changelog.

My plans for 1.0 are primarily to take advantage of the extensible content types added in 0.8 and add some sort of tumblr-like auto-embedding support. But I probably won't get around to working on that for a spell. Why?

Other Lispiness

Because my lisp emulation experiment/art project is ongoing. Nyef was kind enough to share some code he'd hacked up for NES emulation years ago and it helped give me the motivation to rewrite famiclom's PPU (Graphics Card). The former code was largely cribbed from Patrick Walton's sprocketnes and I didn't understand it very well. I've hit the nesdev wiki again and am getting more comfortable with the PPU's actual workings. The code is on github in the new-ppu branch and I'm hoping to spend more time on it this coming week.

I also spent the last week porting cl-6502 to clojurescript for giggles. Heresy, I know. ;)
cljs-6502 is in a basic working state but there are bugs aplenty and I haven't implemented the assembler or disassembler. The must frustrating part was dealing with A) differences in macro hygiene and B) poor macro debugging facilities.

The browser is a fun target though. I'll have to try parenscript or ... jscl! JSCL is a full CL->JS compiler in early development, which I contributed a tiny patch to for fboundp. It's a great project and if you have any interest in helping implement a lisp, I'd encourage you to get involved. The maintainers are very approachable and there's plenty of fun hacking to be had.

All for now. It's time to play around trying static analysis of Nintendo ROMs with Lisp. I'm bound to learn something...hopefully.

So Close and Yet So Far
posted on 2013-03-16 12:22:00

Famiclom Progress

"Low-level programming is good for the programmer's soul." - John Carmack, via ahefner

"What I like about Lisp is that you can feel the bits between your toes." - Drew McDermott, via Michael Weber


I never did enough systems programming. In college, I actually convinced my Operating Systems professor to let me do the course project in lisp. So when I decided I wanted to get closer to the metal a year ago, I thought I'd look into Nintendo emulation with Common Lisp rather than systems hacking with C. Besides, my needs for a web server or other daemons were filled. So I embarked on that weird journey and came out with a shiny, readable, reasonably fast 6502 CPU emulator in under 800 lines of code. It even has an assembler and disassembler!

Announcing Famiclom version least-positive-fixnum

But a CPU emulator isn't much fun. No graphics, no sound, no I/O! After a break from September through January I got back to work in earnest a month ago. It started with getting Klaus Dorfmann's exhaustive correctness tests for the CPU added to my testsuite and a lot of bugfixing. Then I used pcwalton's lovely Rust code as inspiration and started getting the memory mappers and PPU (graphics) working with lispbuilder-sdl. So far we only support NROM mapped games though MMC1 should be coming soon(tm). As you can see at the top of the post, there are still some rendering bugs to work out. All testing so far has been done on CCL and SBCL on Linux.

Current Status

The good news is that the CPU, PPU, and .nes file reading are all done in ~1570 lines of Lisp code! The CPU in particular I think makes for quite nice reading at this point. The main NES code still needs work. The bad news is that while the CPU runs at 2-3x the speed of the NES the graphics are about 15-20x slower so I'm going to have to spend some time optimizing. I'm in #lisp on freenode regularly and would love advice or patches from any low-level SBCL or lispbuilder-sdl hackers. :)

Where to next?

  1. Preliminary input handling is written, hook it into the main event loop.
  2. Finish MMC1 loader. Get Mega Man 2 title screen loading at least.
  3. Fix rendering bugs and try to play a few games.
  4. Optimize and/or add audio support!
Lessons from Coleslaw
posted on 2013-01-06 14:40:00

Is there anything more pointless than a new blog engine? Probably not. 4 months ago, I wouldn't have thought that I would be distracted from my Lisp 6502 emulator so long or that I'd have this much fun writing blogware. It is amazing, however, just how much you can do with a bit of time and ~600 lines of lisp.

Lately I've come to realize my favorite part of hobby programming is that I essentially treat it as creative writing. One of the reasons I love Lisp and find myself using it so much for hobby code is how easily it enables me to experiment with new coding styles. In Coleslaw's case, this has meant a stronger focus on CLOS and API design.

I like to think there's a clear stylistic shift in my projects, from the earlier and messy imperative of Paktahn, through the neat but overly macro-heavy cl-scrobbler, to the more balanced style of my present day code. It's no surprise that some of my favorite lisp luminaries, Peter Seibel and Luke Gorrie, talk a lot about code as literature and readable programs. Hopefully, I will continue to progress in that tradition.

Coleslaw 0.8 is hereby released. The biggest features are multi-site publishing and support for new content types. Here is an example bookmark or tweet-like content type that may ship in a future release, Shouts. See the NEWS for further details. It's time to get back to Memory Mappers for a bit and see if I can't get actual NES emulation going in pure Common Lisp. See you next time, Planet Lisp.

Now with even more Lisp!
posted on 2012-09-19 20:47:00

I haven't finished my headless NES emulator in time for Strange Loop. On the other hand, I have done some cool things that I didn't anticipate. Here's what's been going on in hackland lately:

Coleslaw: Heroku & Plugins

The majority of my efforts have been related to my new blogging engine, Coleslaw. I've substantially cleaned up the rendering pass, added optional RSS feeds for specific tags, revamped the plugin architecture, and added a plugin for Disqus support. Jose Pereira also wrote a heroku buildpack for running Coleslaw so if you feel like having a simple managed install, problem solved!

While docs are still needed, here is a rough overview of the plugin architecture. I'll add a simple, hello-world-ish example to the README shortly.

  • Plugins are lisp files placed in coleslaw's plugins directory.

  • Each plugin should define a package :coleslaw-$filename where $filename is the name, excluding extension, of the plugin.

  • The package should export a function named enable that can be called to activate the plugin.

  • enable is mostly useful for adding Javascript to the page via add-injection or passing initialization args elsewhere.
    • add-injection takes a cons like (js-string predicate) and a location (:head or :tail) to insert it.
    • The predicate should take a single content object as argument. A content object can be either a POST or an INDEX.
    • The predicate will be called at render time and a non-nil return value will cause the injection to be included in the page.
  • Plugins can also extend render-content to support new post formats such as ReStructuredText or modify deploy with :before, :after, or :around methods to support deployment to S3, serving via Hunchentoot, etc.

  • End users take advantage of plugins by enabling them in their .coleslawrc's :plugins list.
    • A plugin given as a symbol will call enable with no args whereas a plugin given as a list will call enable with the args after the plugin's name.

Colorize Reborn

I am pleased to announce I've taken over as maintainer of colorize. It provides the syntax highlighting in Coleslaw's 3bmd markdown mode. I've backported patches from lisppaste to colorize for Haskell, Erlang, Python, and a number of other languages. I also added very rudimentary support for Clojure highlighting. While I'm interested in seeing further language support (particularly Clojure and Rust) I lack the time to work on further coloring modes myself. If you have any inclination to hack on colorize to add support for new languages or otherwise improve it please feel free to contact me. I'm more than happy to review and merge pull requests. :)

Wanting Types, Demanding Mirrors

I delivered a final Lunch and Learn at CMGdigital on Dynamic Systems. I have a screencast of it like my last talk but I haven't uploaded it yet. I'm a bit more out of my depth this time and am still considering tweaking the content and rerecording. The slides are linked above though and I would welcome comments. I'm also working on a Magic the Gathering tutorial/unsession for Strange Loop and an Emacs Crash Course for my new coworkers at Primedia. Finally, I'm giving a talk on the internals of cl-6502 to the Atlanta Lisp User Group on October 1st.

Vacietis and trivial-dump-core

Vladimir Sedach has been working on a C to Common Lisp compiler called Vacietis for a while now. It's become mature enough to generate Lisp executables for small C programs. However, dumping executables isn't a portable CL feature so I contributed a minor pull request to use trivial-dump-core to improve portability from ccl to clisp, sbcl, and ccl. I hope trivial-dump-core sees more use and gains support for more implementations as portable executable creation would be a nice thing to have.

Swanky Developments
posted on 2012-09-04 13:22:05

Now that the i's have been dotted and the t's crossed I'm pleased to announce I've accepted a new job. Starting September 17th, I'll be a Senior Developer working for Primedia. I'll be helping them migrate from ruby to clojure. I've been meaning to spend more time hacking Clojure as it is. I'm particularly delighted that I'll be in something of a teaching role and able to share my knowledge and experience with lisp with interested hackers.

CMGdigital has been a phenomenal place to work for the last year and I'll miss everyone there dearly. I wasn't looking for a new job but Primedia found me and this was in many ways the right opportunity at the right time.

I'm also very excited for the arrival of Leiningen 2.0 and happily running the latest preview. After using quicklisp, I disliked having to setup a mock project to experiment with arbitrary libraries in Clojure. Leiningen 2 uses a library called pomegranate under the covers which allows modifying the REPL classpath. Thus, dependencies can be easily added to a running REPL and experimented with!

In other lispy news, the dream of endless swank backends and SLIME on everything has died. Previously, I had coerced SLIME into running Clojure, Scheme, and Common Lisp simultaneously and knowing which filetypes to associate with which repls. It took a lot of fiddling. I actually had a rant against the proliferation of swank backends for other languages like Chicken Scheme and Clojure happening outside the main SLIME tree. Anyway, between Emacs 24 shipping package.el, marmalade, nrepl.el for Clojure, and Geiser for scheme, the situation has resolved itself even if the infinite SLIME dream is dead. And ultimately, that's better for hackers who am I to complain? :)

Coleslaw Lives!
posted on 2012-08-26 12:42:00

New Beginnings

So, Coleslaw is alive (you're looking at it) and I've done a clean reinstall on my server for the first time since 2008 or so. Thank GOD.

With any luck, I'll get back to hacking emulators now. :) But first... a test of some features! I should really overhaul the README for coleslaw too.

;; God do I love being able to write this post in emacs. And commit and push to publish.
(defun slug-char-p (char)
  "Determine if CHAR is a valid slug (i.e. URL) character."
  (or (char<= #\0 char #\9)
      (char<= #\a char #\z)
      (char<= #\A char #\Z)
      (member char '(#\_ #\- #\.))))

(defun slugify (string)
  "Return a version of STRING suitable for use as a URL."
  (remove-if-not #'slug-char-p (substitute #\- #\Space string)))

A LaTeX/mathjax test...

$$ \lambda \scriptstyle{f}. (\lambda x. (\scriptstyle{f} (x x)) \lambda x. (\scriptstyle{f} (x x))) $$

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