Sunday, December 30, 2007

Scala: first impressions

I'm reading the prerelease of the Scala book, since I'm working for a heavily Java-invested organization now and programming in Java feels like running a race with cement shoes. Politically, Jython doesn't seem like an option; Scala might be an easier sell.

Here's some of my impressions going through the book.

Scala is a decent scripting language

[updated this section thanks to comments from anonymous, Jörn, and Eric.]

Here's how you can loop through each line in a file: Python:

import sys
for line in open(sys.argv[0]):
   print line
Scala:
import scala.io.Source
Source.fromFile(args(0)).getLines.foreach(println)

The scala interpreter also has a REPL, which is nice for experimenting.

This article has more examples of basic scripting in scala.

Getters and setters

One thing I despise in Java is the huge amount of wasted lines of code dedicated to getFoo and setFoo methods. Sure, your IDE can autogenerate these for you, but it still takes up lines in your editor and effort to mentally block them out when examining an unfamiliar class to determine what it does.

C# has Python-style properties, so in theory could be virtually free of this kind of boilerplate, since there is no syntactic difference between "foo.x = y" whether x is a raw field or a property. So, the right thing to do, which you'll see in Python code, is using a raw public field until you actually need extra logic, at which point you replace it with a property and nobody's code breaks.

But C# wasn't far enough removed from Java culturally so everyone writes boilerplate properties instead of boilerplate getters and setters. (I'm aware that in a compiled language like C# it makes sense to start with properties for classes in certain kinds of libraries but these make up a vanishingly small number of actual classes in the wild.)

This is a long way of saying that Scala's properties make a lot of sense given the audience they are targetting (Java programmers). Scala vars are automatically turned into properties (or getters and setters, if you prefer to think in terms of those). So even the most obstinate fan of boilerplate code has absolutely no reason to keep writing unnecessary getters and setters.

If you need to manually tweak your properties later, you can magically define a setter for "field" by naming a method "field_=". This seems a bit like a one-off hack rather than part of a well-designed system, but I can live with it. (Since parentheses are optional for a scala method taking no arguments, any no-argument method call is already syntactically indistiguishable from a raw field read.)

Scala doesn't know what it wants to be when it grows up, yet

Scala contains a lot of features from a lot of different influences, which means there's often competing styles to use; the young scala community hasn't yet decided which to emphasize. For instance, iteration vs traversal -- "for (item <- items)" vs "items.foreach" -- or even whether to leave out optional (inferred) type declarations.

Perhaps this is merely a failure of one book trying too hard to make scala be all things to all readers.

Random thoughts

  • Scala needs something like Python's enumerate function; if you want to loop each object in a collection but you need its index too, you have to do a manual for loop.
  • Using parenthesis for collection access ("array(0); map("foo"))") makes it unnecessarily difficult to tell if you're looking at a method call or a collection access.
  • The scala stdlib is not very google-able yet; if you don't know exactly the class you are looking for ahead of time, you probably won't find it. For example, when looking for a scala object that could iterate through lines in a file, I correctly guessed the scala.io package, but would never have bothered looking at Source until more googling turned it up in a blog entry.

Conclusion and disclaimer

This is long enough; I'll probably write more as I go through more of the book. Patterns and implicit conversions are particularly interesting.

I was attracted to scala while looking for a sane alternative to Java on the JVM and it looks like scala might "drag Java programmers halfway to Python," to paraphrase Guy Steele. And I'm happy to be corrected on anything I've written here.

Friday, December 28, 2007

Troubleshooting the ps3 wireless network connection, including error 80130128

My father got a ps3 for Christmas, but ran into some problems getting it on his wireless network. The first one was "connection error 80130128" after configuring it to use DHCP. I couldn't google anything useful about this; just a few other hapless victims asking if anyone had any ideas. Fortunately Dad had his laptop there too and noticed Windows complaining that two machines on the network were both using the same IP. So, over the phone, I walked him through setting up the ps3 with a static address:
  1. on his laptop, run -> cmd
  2. ipconfig
  3. Read the "gateway" ip. Put that into his browser to go to his router's admin page
  4. Find the DHCP settings for his router to see what range of IPs it hands out; pick one outside that range
  5. Set up the ps3 with that IP, the router IP as primary dns, and an opendns server as secondary
This made the connection test happy. But when he tried to go to the playstation store, it gave a DNS error. If he repeated the connection test again, it failed too. "Well," I told him, "It's supposed to try both DNS servers. But we can try setting the primary DNS server to opendns as well." Once he did that, everything worked.