C[omp]ute

From: andrew cooke <andrew@...>

Date: Sun, 27 Sep 2009 15:35:39 -0400

I just decided to do a quick + dirty project - I want to run through
my mp3s, read the tags, store everything in a database, and then pull
tags from the last.fm API so that I can automatically construct
playlists of related music.

I also decided the time has come to learn Scala.  I could do this
easily in Python, but I've been postponing Scala for too long.

I looked at Scala yesterday and downloaded the port of processing,
which used sbt (Simple Build Tool).  I was thinking about looking at
ant+ivy (something else I need to learn), but I *think* sbt uses ivy
under the hood (or uses Maven, or all share the same basic
infrastructure).  So for now I am going with sbt.
http://code.google.com/p/simple-build-tool/ (which I had installed
yesterday).

So, first step was to create a new directory and run sbt.  It asked if
I wanted to create a new project and I said yes, and gave it a name.
Now it seems to be downloading stuff.

OK, so that left me with some basic directories:

spu63 uykfd: ls
lib  project  src  target

OK, now how do I make that work with Eclipse?  No idea.
http://code.google.com/p/simple-build-tool/wiki/IntegrationSupport
suggests using IvyDE (note - I have already installed the Scala plugin
in Eclipse).  So I install this via
http://www.apache.org/dist/ant/ivyde/updatesite

reload + deliver-local in sbt (following instructions at
IntegrationSupport link above).

I still don't get this.  I think I need to create the Scala project
first in Eclipse, so move the directories generated with sbt above out
of the way, create the Scala project from within Eclipse, and then
move the sub-directories back.

But Eclipse is using Scala 2.7.6 and sbt is using 2.7.5

So delete those and in the project directory created by Eclipse run
sbt again, giving the correct Scala version.

That gives an error "unknown resolver sbt-chain" which I am going to
ignore, and otherwise seems to have worked.

F5 to refresh Eclipse and we seem to be cool.

Run reload and deliver-local again in sbt.  F5 again in Eclipse and
add library as described in link above.  Looks good.

Next I create a HelloWorld class in the main.scala package, based on
http://www.scala-lang.org/node/166 but when I try to run it in Eclipse
it is treated as "HelloWorl" (no final "d") and so fails!

If I fix that in the run configurations I then get
Exception in thread "main" java.lang.NoSuchMethodError: main
which sucks somewhat.

This is not looking good.

Running via sbt gives something similar.  Does the "main" have to have
a special name?

I checked with the example and had "class" rather than "object";
fixing that doesn't seem to change anything in Eclipse, but now sbt
works:

> run main.scala.HelloWorld
[info]
[info] == copy-resources ==
[info] == copy-resources ==
[info]
[info] == compile ==
[info]   Source analysis: 1 new/modified, 0 indirectly invalidated, 0 removed.
[info] Compiling main sources...
[info] Compilation successful.
[info]   Post-analysis: 2 classes.
[info] == compile ==
[info]
[info] == run ==
[info] Running main.scala.HelloWorld ...
hello world
[info] == run ==
[success] Successful.
[info]
[info] Total time: 2 s

Trying with the syntax at http://www.scala-lang.org/node/94 also works
with sbt, but not with Eclipse.

Looking at the comments for Application (via Eclipse F3) it seems it's
not recommended.  So revert to earlier syntax:

package main.scala

object HelloWorld {
  def main(args: Array[String]) {
    println("hello world")
  }
}

Which seems identical to the example.

Andrew