MySWT.scala

import org.eclipse.swt._
import org.eclipse.swt.layout._
import org.eclipse.swt.widgets._
import org.eclipse.swt.events._

object MySWT {
  def main(args:Array[String]) = {
    val display = new Display()

    val shell = new Shell(display)
    shell.setText("MySWT")
    shell.setSize(200, 100)
    shell.setLayout(new GridLayout());

    val l1 = new Label(shell, SWT.PUSH);
    l1.setText("Hello");

    shell.open()
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        display.sleep()
      }
    }
    display.dispose()
  }
}

Rakefile

SCALAC = 'scalac'
SCALA = 'scala'
JAVACMD = '/System/Library/Frameworks/JavaVM.framework/Versions/1.5.0/Commands/java'
JAVA_OPTS = '-XstartOnFirstThread' 
CLASSPATH = %w(
  /Applications/eclipse/plugins/org.eclipse.swt.cocoa.macosx_3.5.0.v3550b.jar
)

PROJECT = 'MySWT'
SRCS = FileList['*.scala']

def opt_classpath
  classpath = CLASSPATH
  classpath.unshift('.')
  "-classpath \"#{classpath.join(':')}\""
end

task :default => ['compile', 'run']

task 'compile' do
  sh "#{SCALAC} #{opt_classpath} #{PROJECT}.scala"
end

task 'run' do
  sh "env JAVACMD=#{JAVACMD} JAVA_OPTS=#{JAVA_OPTS} #{SCALA} #{opt_classpath} #{PROJECT}"
end