This Statement Is False

According to my only somewhat extensive automated tests, Milestone 1 (Basic Xus) is now complete. That includes layers 1 and 2 and the property service (transient and persistent properties). Plexus relies heavily on its property service (currently backed by FreePastry) and I think it will be useful to other programs as well. It's kind of a persistent broadcast; it's really just for relatively small databases, like if you have to track a few hundred things for the topic, like player locations in a game or account credit, for instance. Plexus uses properties for player presence (nickname, which world they're connected to, etc.) and object information (location, orientation, costume, etc.) If you need to store large amounts of data, it might be appropriate to use the file storage service (coming soon and featuring optional Git integration) or maybe to add a database service (and contributing it back to the project would be nifty, too). DHT message routing is useful for ...

Xus has a 2-pronged approach for integrating its file storage with Git: the basic file storage will just use ordinary file storage, with an approach similar to Git's, ensuring that Xus' model is "compatable" with Git's provide a plugin that uses JGit (http://www.eclipse.org/egit/) for people who want to maintain a local Git repository Each peer can be optionally Git-enabled, since the peers will only interact with a local Git repository. It doesn't use Git's protocol to exchange data, because we want Xus to be able to swarm downloads, but a Git-enabled peer could use Git-clone to seed its cache. Since the file storage protocol doesn't have to interact with Git, Xus just needs #1 to make sure that a peer can fetch everything it needs over the net. Since Git uses SHA-1 hashes as keys for almost every type of object, this shouldn't bloat the protocol too much. Note that when I say "protocol" here, I'm talking about the file storage...

I have layers 1 and 2 working now, with automated tests (it's on github). Layer 1 is simple packets and layer 2 is p2p messaging. That covers: strong authentication (challenge/response on connect with RSA keys & signatures) direct peer-to-peer messages broadcast messages unicast messages dht messages (delegated to the peer with the peer id closest to the dht key) delegated peer-to-peer messages (one peer sending to another peer through a topic) Right now, as long as your peer doesn't spoof its public key, it can connect to any topic (authorization is part of layer 3). I think one other thing I should add to layer 1 is a heart beat, so you can quickly detect dropped connections (TCP timeouts are notoriously unreliable). Layer 3 is the service layer and has these components: Properties Topic authorization and management (including peer "accounts") File sharing Port configuration testing Connect-back requests (for when only one peer can accept connections) A note...

When I saw Dude Where's My Car?, several years ago with my wife (who is Chinese), she started laughing right as they pulled into the parking lot of a Chinese restaurant . I had no idea why, but she said to wait until the end of the scene. In the scene, after they order each item, a voice from the speaker says, "and then?" and continues after they run out of things to order until Ashton Kutcher eventually destroys the speaker in frustration. When the scene was over, I asked her why she started to laugh at the beginning of the scene. She said she had heard people quoting that at work, but she never realized that the Chinese name of the restaurant, which she saw at the beginning of the scene, was "And Then." Appropriately, Scala defines infinite loops in actors using andThen. Here's how... In Scala, one way to compose functions is "f andThen g", which is the same as def newFunc[T](x: T) = g(f(x)) You can think of it as "evaluate f(x) and the...

A friend of mine wanted to implement peer-to-peer source code repositories with social networking features, like popularity ratings and such and Plexus was already on the way to being able to support something like that, so I decided to break out the back end of Plexus into a separate project, called Xus. We started talking about what such a thing could do. Then the bottom fell out of Plexus. Apparently, the FreePastry project is winding down. It was, in my opinion, the most promising of the major peer-to-peer platforms. It was straightforward and relatively small. We chose it over JXTA for our communication in Plexus. We actually started with JXTA, back in 2002, but JXTA was just too over the top with the excessive design patterns, the large surface area, the lack of a usability layer, and things of this nature. Why does Sun seem to delight in requiring so much ritual from developers to do the simplest things with their libraries? So Pastry is way cleaner than JXTA. Like JX...

This post on Scala-lang talks about research done on how the style of language affects productivity (the time it takes to understand other peoples' code). It is specifically comparing Java with Scala. Here is the paper that the post refers to. Scala allows functional programming, as in Scheme, as opposed to procedural or object-oriented programming, as in Java, but Scala allows a nice blend of the two, which is a unique approach among programming languages. Yes, there was LOOPS and CLOS, but Scala's approach is quite different and I think it's much a more integrated one. There seem to be more and more posts out there about the importance of functional languages. Personally, I agree with the premise: that functional techniques lead to denser code and that can be (if used properly) easier to understand and maintain. Actually, this is related to one thing that I emphatically agree with the eXtreme Programming camp on: don't use accessors unless absolutely necessar...

Dot #1: Lambda Calculus... My wife and I took a vacation recently and I had a chance to learn some more Lambda Calculus; how the Y-combinator works, in particular. At Purdue, we focused on Turing Machines and either we didn't really cover LC or I slept during that part. If you haven't, I HIGHLY recommend learning LC. Lambda Calculus is the most elegant system I, personally, know of (maybe that's not saying much). You functional-types out there will already know this next part, but here's some history and stuff. It was invented by Alonzo Church, who was Turing's Ph. D. adviser (later they proved that the Lambda Calculus and Universal Turning Machines are equivalent, which was one really impressive feat). The Y-combinator is a way to define recursive functions using only lambda binding. Lambda binding is very simple and it's pretty much what Lambda Calculus is. It more or less just lets you assign values to variables and then use them in an expression, lik...

I noticed these in walking around in Jerusalem and I haven't seen a lot about them on the web yet, so I thought I'd post them. The last one's a fake, obviously put up by a concerned citizen who thought that werewolves weren't getting the representation they deserved. There are several more that I haven't photographed, including at least 2 more fakes: a man dragging a baby, and an angel as well as at least two authentic ones, a man with one hand in a fist and the other with fingers spread and a fat man. I'll post those eventually.

I made some changes to Ober that make it quicker to use. Now, when you right-click a word, Ober does everything in path-like fashion: if the word is an Ober built-in, execute it if the word is a class name, run the main with the args to end of line if the word is a shell command, run it if the word is a file, directory, or URL, open it If you middle click, that sets a hint to tell the command that if it is appropriate, open a new viewer instead of replacing the current one. Also, I made a runnable jar for it all, so you don't have to build it. Here's the new doc page

After spending 4 or 5 years working on servers with decent amounts of data going through them, I've had to do a fair bit of forensic work with saved databases, giant log files, etc. AWK, sed, Groovy, EMACS, and their kin have been my friends. You can use them to distill unstructured text into a structured form for summaries, trending, etc. I am starting to turn Ober into a console for this type of forensic work. I can see how farsighted Niklaus Wirth was when he made Oberon. This doesn't look to me like a temporary phase in computing. If anything, unstructured text is even more prevalent today than it has been in the past. Google has shown people what you can do with it. We'll see where Ober goes from here. For the future, I'm planning on adding some more Wily-like features to Ober, like preceding commands with |, . Here's an update on Ober... Ober is becoming usable now. Here are the items I checked off of the list from the last post: execute HOME/.oberrc ...

If you haven't heard of Niklaus Wirth's Oberon or you haven't seen it, you should check it out. Messing with it reminded me of when I first learned Smalltalk in 1988. There's an air of playfulness and potential to it, just like in Smalltalk-80. The current version of Smalltalk is called Squeak and it's well worth checking out as well. Oberon is sort of a Pascal take on Smalltalk. Like Smalltalk, it's both a language and an environment. Like Smalltalk, it has built-in programming tools (compiler, editor, etc), and it's interactive; you're programming "in" the language, so the edit-compile-run cycle is VERY tight (like when you're using the scala command and you can evaluate expressions). Oberon's environment was similar to Smalltalk's, but had some major differences and innovations, the most valuable one being (in my opinion) that you can click on a word anywhere in the environment and it will attempt to execute it as a comma...

Wow, I sure stirred up a hornet's nest with my safe navigation experiment. Some people posted some very useful information and good alternative approaches! As for comments about "ugliness", being able to read this in 6 months, etc.; I'm not making a policy decision here, just experimenting. The fact that people are so put off by experimentation makes me wonder... Anyway, we'll see if it comes in handy or not. Things like this can easily be "compiled" by the mind as "programming idioms". But as for unreadable, it's only a cascade of lambdas, after all. Personally, I've been very comfortable with functional style, since I first learned LISP, freshman year in college. It's amazing to me how emotional some programmers get when they see code using functional style. Does this mean "imperative -> good, functional -> bad?" I guess there's always been a divide between functional and imperative approaches. I'm ...

OK, revisiting this topic after a very short time, I have a new implementation, again using that interesting anonymous class technique from James Iry's comment: implicit def richOption[T](x : T) = new { def ??[B](f : T => B):B = if (x != null) f(x) else null.asInstanceOf[B] } I changed the operator from "?!" to "??" because that's a lot easier to type and I chose "??" instead of "?" so people wouldn't confuse it with the questi-colon operator from Java and C. It's stand-alone (doesn't depend on Option or anything) and I had to use a cast to get the types to work out properly, but the test case from my last post does work println(p3??(_.bud)??(_.bud)??(_.bud)??(_.name.drop(1))) prints null and println(p3??(_.bud)??(_.bud)??(_.name.drop(1))) prints ubba. For those new to Scala, the expressions in parentheses are anonymous functions because they use "_" as identifiers. (_.bud) expands to (x => x.bud), where Sca...

Welcome to my first blog post. I searched the net for a Scala analog to Groovy's safe navigation, but I didn't find anything, so I made my own. It's like a monad but I haven't thought much about the implications of really making it into a real monad so I haven't monadized it at this point. Here is some example data to demonstrate how you use these safe navigation operators in Scala: case class Person(var name: String, var bud: Person = null) val p1 = new Person("bubba") val p2 = new Person("fred", p1) val p3 = new Person("mary", p2) println(opt(p3)?!(_.bud)?!(_.bud)!(_.name.drop(1))) This code prints "ubba". It uses ?! like Groovy's ?. operator (?. isn't a legal operator in Scala because of the .), but you need the extra parentheses or it doesn't parse like you would want (I think Scala needs the parentheses to disambiguate the scope for the _). The final ! operator returns the closure value instead of wrapping ...