example_controller.rb

class ExampleController < Adhearsion::CallController
  def start_recording(call)
    call.record :async => true do |event|
      # This code will execute when the recording is complete (when the call ends)
      logger.info "Your recording is at #{event.recording,uri}"
    end
  end

  def run
    dial "SIP/#{@dial_num}", pre_join: &:start_recording
  end
end

The error is still present although I do it from the gist or I type it all instead of copy paste:

WARNING: Nokogiri was built against LibXML version 2.9.1, but has dynamically loaded 2.8.0
Starting Adhearsion server at /home/ano/myapp
script/ahn: /home/ano/myapp/lib/example_controller.rb:15: syntax error, unexpected & (SyntaxError)
dial "SIP/3001", pre_join: &:start_recording