Add a simple example of declaring an interface.
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#
#      http://www.apache.org/licenses/LICENSE-2.0
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import java.util.List

interface Printer do
  def printAll(a:List)
    returns void
  end
end

class MyPrinter
implements Printer
  def printAll(a)
    a.each {|element| puts element}
  end
end

list = ['foo', 'bar', 'baz']
p = Printer(MyPrinter.new)
p.printAll(list)