gistfile1.scala

package a

import org.codehaus.griffon.runtime.core.AbstractGriffonModel

class AModel extends AbstractGriffonModel {
    var input: String = ""
    var output: String = ""

    // must make getters/setters explicit so that the Griffon runtime
    // can call the appropriate method. Scala follows a non-JavaBeans
    // convention for defining properties

    def getInput():String = input
    def setInput(in: String) = firePropertyChange("input", input, input = in)

    def getOutput():String = output
    def setOutput(out: String) = firePropertyChange("output", output, output = out)
}

You might want to use @BeanProperty instead of the explicit get/get function pairs.
http://www.scala-lang.org/api/current/scala/reflect/BeanProperty.html

I did but sadly @BeanProperty is not smart enough to figure out that I have written a custom setter and fails with a compiler error stating that setInput() has been defined twice!