[AS2] Function parameters default values


How can I set default values for the parameters of a function in AS2?
I am trying the common way but it doesn’t work…

private function myFunction (param1:Number = 3, 
                      param2:String = "a string", 
                      param3:Boolean = false, etc ....):Void

I’m pretty sure I’m doing something wrong but can’t figure it out.
I’ve searched but found nothing on adobe’s reference’s. Tried the forum search but returned nothing although I’m sure this would be one more duplicated topic… sorry for this and thank you for your help.