leah blogs: December 2005

With all the rage for reasons whatsoever about Ruby and its Symbols, people often start to compare Ruby symbols with Lisp symbols. Don’t do that, it’s just wrong.

Ruby symbols are not Lisp symbols!

There are at least six important differences:

For Lisp symbols, the Common Lisp Hyperspec says (in this post, Lisp is considered to be Common Lisp):

Symbols are used for their object identity to name various entities in Common Lisp, including (but not limited to) linguistic entities such as variables and functions.

Symbols can be collected together into packages. A symbol is said to be interned in a package if it is accessible in that package; the same symbol can be interned in more than one package. If a symbol is not interned in any package, it is called uninterned.

About Ruby symbols, ri says:

Symbol objects represent names and some strings inside the Ruby interpreter. […] The same Symbol object will be created for a given name or string for the duration of a program’s execution, regardless of the context or meaning of that name.

This is the first imporant difference: Ruby symbols are globally unique, Lisp symbols can exist in several packages. This means that there can be symbols in Lisp which have the same name but are different: FOO and FOO will always be the same, but a symbol FOO given in package A to a function in package B will not be equal to FOO there. This can easily confuse newbies.

Second difference: Lisp symbols can be uninterned, whereas Ruby symbols only exist when they are interned. (An exercise to the Ruby curious: Find out how to check if a symbol with given name exists, without interning it. Answer below.)

Third difference: Lisp symbols carry data, Ruby symbols only identify. A certain Lisp symbol has two slots, a value cell and a function cell. Since Common Lisp is a Lisp-2, a symbol therefore can “be” a variable and a function at the same time. Ruby symbols aren’t anything, but they can be used to lookup methods (but not local variables, despite Ruby also being a Lisp-2… and for instance variables, don’t forget the @).

Fourth difference: Lisp symbols have a property list, Ruby symbols don’t (but you could add that). Imagine a Lisp property list like instance variables in Ruby. Property lists often are used to attach data to symbols (this was used for the first object-oriented programming styles, a.k.a. “flavours” in Lisp, for example).

Fifth difference: Lisp symbols can get garbage-collected if they are unbound, Ruby symbols stay alive forever. This can be considered an implementation detail but has to be kept in mind if you intern a lot in long running processes. (Don’t!)

Sixth difference: Lisp symbols are upcased automatically by default, Ruby symbols are created as specified. Basically, foo and FOO is the same in Lisp, but :foo and :FOO aren’t in Ruby. To create something like :foo in Lisp, you’d need to write |foo|.

These differences make clear that Lisp symbols are rather different to Ruby symbols, but there is one “exception”, the Lisp symbols of package KEYWORD. Now, guess how these Lisp symbols are created… exactly: with a leading colon. The Lisp symbol :foo is a symbol called “FOO” in the package “KEYWORD”. Therefore, the Lisp symbol created given by :foo always is the same as :foo. Keywords are mainly used for keyword parameters (cf. Rails), where the calling package often isn’t the definiton package.

I conclude:

Ruby symbols aren’t Lisp symbols, but Lisp keywords.

Answer to the exercise:

puts "U3ltYm9sLmFsbF9zeW1ib2xzLmFueT8geyB8c3wgcy50b19zID09IGdpdmVu
X25hbWUgfQ==\n".unpack('m*')

NP: David Gilmour—Terrapin

Nukumi2 0.5 is released.

This is the second release of Nukumi2 since exactly this day last year. Nukumi2.5 (or, for technical reasons, Nukumi2 0.5) is primarily a maintenance release fixing some small bugs; the biggest change is the switch from Needle to Dissident for dependency injection. This change will require you to do a minor change in your config.rb.

Nukumi2.5 is one of the bug-fixing releases before Nukumi3, which will never exist. Instead, Nukumi2.5 will slowly converge to Nukumi2.5029078750, which is the second Feigenbaum constant.

What’s new in Nukumi2 0.5?

• Atom 1.0 support (thanks to Sebastian Vuorinen)
• Using Dissident for dependency injection instead of Needle
• Works with Ruby 1.8.3+

This release does not incorporate the Kashmir templating engine yet, just because I lack the time to rewrite the templates.

You can get Nukumi2 0.5 at: http://chneukirchen.org/releases/nukumi2-0.5.0.tar.gz

Merry blogging and a happy new year. :-)

NP: Bob Dylan—I Shall be Released

Maybe you already saw my yearly christmas greeting on ruby-talk:172428 (last year’s to be found here), but today I’d like to explain how I did it. If you didn’t run it yet, do that now and be amazed. ;-)

First of all, I needed to implement the actual logic. I’d only like to outline it here and leave the rest for the reader. You may want to read the complete, unobfusciated source.

The real snowfall happens in snowdrop!, where a random vector of snow heights gets increased by one in a way the difference to the neighbour elements is never greater than one. This vector then gets rendered in to_s onto a marshalled array with the greeting message by differentiating the vector and thereby figuring out which chars to use. Above the skyline snow randomly gets painted.

All this happens until all the vector’s elements are filled up. The logic is not very difficult but I tried quite a few ways to make it work best. I’d like to thank Frixon on #ruby-de for the inspiration; he had to write the mountain algorithm in Ada (I didn’t look at the code, only at the output).

Of course, that was the easy part. ;-) Now, the thing had to be styled. Since this years hack was a lot bigger than last years (2221 byte), I couldn’t simply reuse last years fir tree. I first tried to add some thicker border to it, but then I thought it would be boring if I used the same image twice.

So I took the PostScript star of first advent, gimped it a bit (solid fill, rescaling to an appropriate size and ratio since terminal fonts aren’t 1:1), then saved it into a portable grey map and solarized it into ASCII chars using a self-written script. The rest of the image (border and snow) was made manually using Emacs’ picture-mode.

The final ASCII image, consisting of * and and some custom text was then filled with code, using a similar script like last year.

It was some hours of work, some hours of fun and I hope you enjoyed it!

NP: The Melvins—Revolve

Frohe Weihnachten, ein schönes Fest, und einen guten Rutsch ins neue Jahr wünscht euch Christian Neukirchen

Merry Christmas and a Happy New Year!

(source)

NP: Die Roten Rosen—Merry X-Mas Everbody

For a bigger school project I recently had to make some outlines. I used the OPML Editor for that, because it’s the only outliner I seriously can use (despite all efforts to write one for Emacs on my own, but more on that below). After all, it wasn’t a bad experience; the outlining is quick and straight-forward and just works. The keybindings are comparatively sane, and the OPML Editor is open source.

Then, I decided I would like to print out the outline. Hehe.

Of course, the OPML Editor doesn’t have a print function. I don’t even expect that actually. However, the only way to get your data out of it is the HTML export. Good, the HTML looks very basic, the HTML is very unclean ([Winer rant suppressed]) and invalid. I also needed to add a title because I had to turn it in.

Trying to do this the “Macintosh Way”… let’s copy the outline (essentially, a nested <ul>) from Safari and paste into Pages. The indentation got lost. Enough, let’s do it the “Unix Way” and edit the generated HTML on my own. I hacked some <h1> in there and quickly had it how I wanted it. Add some CSS styling and the thing is ready to print.

The next time I had to prepare a similar outline, I thought that the OPML Editor provides an almost perfect way to write. You can easily group related paragraphs and so on. All it lacks is a way to declare some outline entries to be shown as titles (and display them in a different style), or as block-quotes or similar. With a bit of thinking on, it would turn out to be a graphical Vooly editor.

I looked around if someone already had that idea (apparently not, which I think is interesting.) Essentially, what I wanted to do is tagging the OPML entries, and the OPML “specification” ([Winer rant suppressed]) even has the type= attribute that could be used for this (alternatively, I’d have added one).

Marked-up Outline: An outline which entries can be of different types and are displayed accordingly.

It’s a bit like that style selector known from popular word-processing (yuck) applications.

Given a marked-up outline, useful things can directly be made from it:

• A XOXO-version (a.k.a., [Winer rant suppressed]) that has appropriate class= attributes and easily can be styled using CSS however you want.

• A properly typeset version for printing, for example using ConTeXt’s XML facilities or some custom code to map the markup tags to TeX.

• Filtered outlines, which only contain certain parts. This could be used to work around limitations of hierarchies.

• and likely something nifty I didn’t think of…

Today, I decided to try implementing it, and dug into the OPML Editor.

This post was written using Emacs.

The display part of the OPML Editor is very hard to customize. Basically, the only thing that can be changed easily is the icon next to the entry, which is not enough for my purposes. If you have used the OPML Editor, you may have noticed it actually does style basic HTML (this was added in Frontier 7.0), for example it makes <b>foo</b> look bold. I thought I simply could add my own tags to that and only needed to figure out how to save the entry tags in the model.

The model part turned out easy, every node can have certain attributes that directly reflect the <outline> attributes of the corresponding OPML.

But it’s impossible to set the font size and style per-node, at least from UserTalk ([Winer rant suppressed]). The code that styles the basic HTML actually is written in C ([Winer rant suppressed]) and uncustomizable ([Winer rant suppressed]). Also, while searching for that code, I found some code I rather wish I hadn’t seen.

No go. I don’t want to hack C and build my own version of the OPML Editor just to make something like that possible.

I quickly looked into other means of editing outlines, especially browser-based ones. The ones I liked were the free sproutliner, Les Orchard’s experiments and the proprietary iJot. All of them are heavily JavaScript-based and I couldn’t figure out an easy way to extend them. If anyone wants to give that a try, by all means, do it!

For now, I’m deciding to go the “Unix way”. I’ll just add the entry tags directly into the outline entry (still need to figure a convenient syntax) and write some scripts to transform them to XOXO and TeX. Also, I may revive my ideas about an new Emacs mode, because with font-locking all that should be rather easy to do.

It’s a bit sad, I think quite a lot of people would have liked to have an easy program that can be used to create valid and semantic HTML documents based on some easy set of allowed elements…

NP: David Gilmour—Wish You Were Here

Dritter Advent, heute endet der Weihnachts^WChristkindlesmarkt in Biberach. Weihnachtsstimmung kehrt zumindest bei mir trotzdem nicht ein, auch wenn hier dauernd Die Roten Rosen laufen. Vielleicht liegts am Schnee, der sich auch schon wieder verflüchtigt/verflüssigt hat—trotzdem bleibt es kalt.

Letztes Jahr am vierten Advent haben wir noch den Gefrierschrank enteist, diese Woche ging unsere Kühlschranktür kaputt und es sah so ähnlich aus. Leider wieder kein Bild gemacht, aber macht nix, man kann ja das von vor zwei Jahren wiederverwenden.

Noch ein-einhalb Wochen bis zu den Weihnachtsferien.

Wenn Weihnachten das Fest der Liebe ist, warum ist dann Weihnachten nur an Weihnachten?
— Engelbert Schinkel

Immer mehr Leute fragen mich, was ich zu Weihnachten will, hat jemand eine gute Idee?

NP: Die Roten Rosen—Ihr Kinderlein Kommet

Just today, my iBook got one year old. lilith, as it’s dubbed, still runs very well, despite of being used just about every day and sleeping the rest of the time. In fact, I can show all uptimes since last December (not counting intra-day reboots):

12 + 19 + X + 19 + 30 + 73 + 106 + 53 + 45

The X represents one bad crash, if you make it 8 days, the sum would be the complete year with 365 days. It think it’s pretty awesome to own an computer that you reboot only nine times a year.

Of course, the case got a few scratches and you can see the places where my hands rest, but it really doesn’t look bad for being used all the year. Apple did a very good job, I once got the battery called back because they feared it would get too hot, but else I there was nothing to complain about. (Not that I’d complain about getting another fresh, new battery for free. ;-))

Not that I would call myself a Mac user now, I still have a Debian box around, and heavily use free software on the iBook. That is, I probably can count the non-free non-OS X-default programs with my fingers (and most are just convenience, if I’d go Debian again I could quickly find replacements, but I don’t really see a reason for that.) Panther is still fairly well supported (I don’t want to buy Tiger), and while that is lasting, I have a very nice notebook that just works.

Actually, I think the only problem I currently have with it is that X11.app doesn’t work anymore after shutting the lid, maybe someone knows what’s going on?

That said, if I had the money, I probably wouldn’t buy an 12.1" iBook again, but instead get the 15” PowerBook everyone seems to own now. And I wouldn’t buy that one if it had an Intel chip inside, either. However, for a nice architecture that is well-supported by the things I use, I’d spend a bit more money than usual.

And now, I shall hack happily until next year’s December 8.

NP: Dire Straits—Private Investigations

I recently stumbled on GotToZ.com, which really is an waste of time but I looked like a challenge, so I tried it for some minutes. The purpose of the site is to tangle through a web of sites, each representing a letter of the alphabet, finally reaching Z. I got up to Y manually, but then I decided Ruby could do that much better than me. I encourage you to try it manually first, though. (Not like you’re wasting enough time already…)

require 'open-uri'

@pages = {}
@count = Hash.new 0

def track(page)
  return  if @count[page] > 2
  @count[page] += 1

  a = (@pages[page] ||= [])
  open(page).read.scan(
      /\074A href="(http:\/\/.*?.com\/)".*?\076[A-Z]\074/m) { |e|
    a.push e.first
  }
  a.uniq!
  a.sort!
  STDERR.puts page
  a.each { |x| track x }
end

track 'http://www.amongothers.com/'

puts "digraph {"
@pages.each { |k, v|
  v.each { |l| puts %Q[  "#{k}" -> "#{l}";] }
}
puts "}"

Run it, possibly a few times because I think the Z site is added randomly (that’s why every page is fetched up to three times, too), and save the standard output into a file. Now, you have a nice graph you can run GraphViz on and do nifty diagrams, like this (click for full 3884x3434 view, be careful):

NP: Dire Straits—Walk Of Life

Excuse the longish post, but I was just part of something great on #ruby-lang, I think this is even better than the zxy___ hack . Enjoy.

20:14   <neoneye>   hi
20:15   <slyphon>   neoneye: nope! too unoriginal!
20:15   <slyphon>   neoneye: now, let's try this again
20:15   <slyphon>   neoneye: you walk into the room...
20:15   <chris2>    with a pencil in your hand
20:17   <chris2>    you see somebody naked
20:17   <slyphon>   chris2: is this where it is?
20:17   <slyphon>   chris2: who is that man?
20:17   <chris2>    you try so hard
20:17   *   slyphon just doesn't understand
20:17   <chris2>    just what you'll say
20:17   *   slyphon gets home
20:18   <chris2>    something is happening in here!
20:18   *   slyphon doesn't know what it is
20:18   <chris2>    slyphon: do you, slypho^Wmister jones?

---

20:18   *   chris2 raises his hand
20:18   <chris2>    is this where it is?
20:19   *   slyphon points to chris2 and says "it's neoneyes"
20:19   <chris2>    what's mine?
20:19   <slyphon>   chris2: where? what is?
20:19   <chris2>    OMG, am i here all alone?
20:20   <slyphon>   chris2: there's something happening
20:20   <chris2>    i dont know what it is...
20:20   <slyphon>   do you? chris2jones

---

20:20   *   chris2 hands his ticket
20:20   *   chris2 looks around
20:20   --- slyphon is now known as the-geek
20:20   <chris2>    =)
20:21   *   the-geek walks up to chris2 
20:21   <the-geek>  chris2: how does it feel, to be such a freak?
20:21   <chris2>    impossible!
20:21   *   the-geek hands chris2 a bone
20:21   <chris2>    something is happening here
20:21   <chris2>    but i dont know what it is
20:21   <the-geek>  do you? chris2jones

---

20:21   <chris2>    i have many contacts
20:22   --- the-geek is now known as lumberjacks
20:22   <chris2>    among #lumberjacks
20:22   <lagcisco>  wereapple: all I need for now is just class methods
20:22   *   lumberjacks gets chris2 facts
20:22   *   chris2 imagines
20:22   --- lumberjacks is now known as slyphon
20:22   *   slyphon has no respect
20:22   *   chris2 gives a check to rubycentral

---

20:23   *   slyphon 's been to the professors
20:23   <chris2>    they liked my looks
20:23   <chris2>    i was at ibm and we talked about sco
20:23   <slyphon>   with #great-lawyers i disussed #lepers and #microsoft
20:23   <slyphon>   hahahaha
20:24   *   slyphon read The Great Gatsby
20:24   *   chris2 has all pdfs of fitzgerald
20:24   <chris2>    and read them
20:24   <slyphon>   chris2: we all know
20:24   <chris2>    something is happening in here
20:24   <chris2>    but i dont know what it is
20:24   <slyphon>   do you? chris2jones?

---

20:24   <douthat>   did I come in at a bad time? :)
20:25   <slyphon>   douthat: not if you like dylan
20:25   <slyphon>   ;)
20:25   <chris2>    slyphon: you need to be the sword-swallower now
20:25   <slyphon>   ah

---

20:25   --- slyphon is now known as sword-swallower
20:25   *   sword-swallower walks up to chris2 and then kneels
20:26   *   sword-swallower crosses himself then clicks his high-heels
20:26   <sword-swallower>   chris2: how it feels?
20:26   <chris2>    here's your throat back, thanks for the loan
20:26   <chris2>    something is happening in here
20:26   <chris2>    but i dont know what it is
20:26   <sword-swallower>   do you? chris2jones

---

20:26   *   chris2 sees a one-eyed midget
20:26   --- sword-swallower is now known as midget
20:27   <midget>    NOW!
20:27   <chris2>    for what reason?
20:27   <midget>    HOW!
20:27   <chris2>    what does this mean?
20:27   <midget>    YOU'RE A COW!
20:27   <midget>    chris2: give me some milk or else GO HOME!
20:27   <chris2>    something is happening in here
20:27   <chris2>    but i dont know what it is
20:27   <midget>    do you? chris2jones

---

20:27   *   chris2 joins again
20:28   <chris2>    coming from #perl
20:28   *   chris2 frowns
20:28   --- midget is now known as slyphon
20:28   *   chris2 puts his eyes in his pocket
20:28   *   chris2 puts his nose on the ground
20:28   *   slyphon thinks about kick-banning chris2
20:29   <chris2>    against me coming around?
20:29   *   slyphon thinks, unless he's listening to his ipod
20:29   <chris2>    something is happening in here
20:29   <chris2>    but i dont know what it is
20:29   <slyphon>   do you? chris2jones

---

20:29   <chris2>    *clap* *clap* *clap* :D
20:29   *   slyphon bows and applauds and bows and applauds
20:29   *   slyphon hugs chris2 :)
20:30   <chris2>    Bob Dylan---Ballad Of A Thin Man (Live Version)
20:30   <chris2>    (by accident :P)
20:30   <slyphon>   totally :)
20:30   <technomancy>   oh man.... i haven't listened to dylan in waaaay too long

Original lyrics: Ballad Of A Thin Man by Bob Dylan.

NP: Bob Dylan—Ballad Of A Thin Man (Live Version)