//If we list all the natural numbers below 10 that are multiples of 3

//or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

//Find the sum of all the multiples of 3 or 5 below 1000.

import scala.actors._

object Adder extends Actor {

var sum = 0

def act() = {

react {

case (num: Int) =>

sum += num

act()

case “REPORT” =>

Console.println(“Total = “ + sum);

}

}

}

object ProblemOneRunner {

def main(args: Array[String]): Unit = {

Adder.start

for(i <- 1 to 999) {

if(i % 3 == 0 || i % 5 == 0 ) {

Adder ! i

}

}

Adder ! “REPORT”

}

}

It starts out looking something like a Java program with an import statement, although Scala uses the _ notation to import everything instead of * since * is an identifier. Scala supports a lot of flexibility in its import statements, they can show up anywhere and you can use them to remap names or set up exclusion filters – but lets not get to far astray.

Next, you’ll notice that my program has two objects and no classes. Its not that Scala doesn’t have classes, its just that Scala classes don’t have the Java concept of static – if you want a singleton object, you use the object keyword. The solution I have above uses one singleton as the main program entry point and another Adder singleton that extends Actor. This is just so I could play with Scala’s built in multithreading and message passing support – obviously this problem doesn’t really require it but I thought I’d try it out anyway for fun.

The Adder has its own sum variable it uses to keep track of the numbers it will add up – Scala uses the var keyword for variables that can be reset and val for ones that can’t. You’ll notice the lack of any type declaration here, its not that Scala variables are not typed, its just that it uses type inference to figure out what they are. Also, Java users will notice the lack of semicolons – semicolons are optional in Scala in most cases. The Adder overrides the act method, the entry point for threads, and then calls react which will look for a message in the actor’s inbox and if it doesn’t find one, put the actor to sleep. Unlike some of the other constructs Scala provides for Actors like receive, the thread will die at the end of react instead of looping so we have to put a call to act() at the end of the int message we send it to keep it alive.

In the main method, we start up our Actor thread, then loop through 1 through 999 looking for numbers divisible by 3 or 5 to send to our Adder, then once we are done we send a message to the thread to report and finish its loop. Again, Java users will notice the easy condensed for loop and the ! message passing syntax.

I’ve barely scratched the surface of Scala here, I’ll try to get a couple more problems done and posted that likewise abuse language features as I get time.

I won’t detail how to setup a dualboot system, there are enough tutorials out there if one searches for them. When I first setup my laptop I installed ubuntu  8.10 and quickly ran into  two annoyances  – an error message about my keyboard layout and the fact that by default the machine is very hard to use since the touchpad causes the cursor to jump around randomly while typing. Not in a mood to research them at the time, I got distracted and sadly it wasn’t until 9.04 that I tried again. Both these problems persist with Jaunty so if you want to run it on your it on your macbook, you are going to run into them.

The first issue manifests itself as an error message stating “Error activating XKB configuration” everytime you log into X. This is related to xorg not apparently knowing what to do with the macbook keyboard variant – there is an umbrella bug ubuntu uses to capture all these types of errors you can find here. The solution is to modify your xorg.conf file to give X more information however I haven’t dinked around with this yet since its just a minor annoyance.

The issue with the trackpad just about renders the machine unusable for anything but the most simplist tasks however its luckily easy to fix (or at least mitigate). In Jaunty, just add a startup application that looks like this:

syndaemon -d

This will start up a program in the background every time you login that will disable the trackpad while you type, preventing it from causing the cursor to jump all over the screen. Syndaemon has a couple more options you can play with such as how long to disable the trackpad for but so far I’m finding the default settings to work ok.

A couple more random hints:

• If you upgraded Jaunty and are now having problems with flash sites like Hulu telling you need flash 9 when you _know_ you had flash installed, try using synaptic to complete remove and then reinstall the flash-installer package – thats what it took for me  to get it working again on my living room media box.

• If you are a quicksilver addict, check out Gnome Do – very slick and the keyboard shortcuts are even the same by default.

JavaBat

Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems.

The motivation for starting Project Euler, and its continuation, is to provide a platform for the inquiring mind to delve into unfamiliar areas and learn new concepts in a fun and recreational context.

I’ve only done the first 4 problems so far so I haven’t even reached “level 1″ according to their scoring yet. Nothing has been all that challenging up to this point, the problems have been taking me around 30-60 minutes to solve. It’s just nice to have a pool of simple programming problems that one can go back to when one is in the mood, sort of like having a book of logic problems laying around.

I had a couple of Xbox S controllers lying around that I haven’t been using. I like the S controllers, they fit my hands nicely and have a good feel to them. I also have a ton of extra USB cables laying around. While browsing around the net I found some instructions on how to splice a USB cable together with the controller cable. In concept, its quite easy since the original Xbox cable is basically a USB cable with a funky connector. Its just a matter of stripping each cable and matching up like color to like color. I practice, the wires in my USB cable that I spliced in were so thin that it was a bit difficult (for me) to cleanly strip them at first without slicing into the wire itself.

A little solder and electrical table later I had a working cable. I had to download drivers for OS X to get it to work on my Mac but Dapper Drake recognized it without me having to do anything.