How to initialize a boolean only once when used in a function when called OnGUI

I've been building a dropdown function to place online for others trying to make something similar. I want to be able to use this same function in multiple instances throughout a GUI. I couldn't find a way to return more than one variable and this will later be return the choice of the menu. Here's what I have so far:

 var show : boolean = false;
 function List(headbox : Rect, dropheight : float, listheader : String, list : String[])
 {
     //reference # for list element
     var selection : int = 0;
     //fullbox starts at the bottom of the headbox
     var fullbox : Rect = Rect(headbox.xMin, headbox.yMax, headbox.width, dropheight);
     if(GUI.Button(headbox, listheader + ": " + list[selection]))
     {
         if(show != true)
             show = true;
         else
             show = false;
     }
     if(show)
     {
         GUI.Box(fullbox, " ");
         for(var l : int = 0; l < list.length; l++)
         {
             var entryystartpoint : float = fullbox.yMin + (l * (fullbox.height/list.length));
             var entryheight : float = (fullbox.height/list.length);
             if(GUI.Button(Rect(fullbox.xMin, entryystartpoint,fullbox.width, entryheight), list[l]))
             {
                 selection = l;
                 show = false;
             }
         }
     }
 }

Sample calling:

 var lister : String[] = new String[4];
 lister[0] = "element 1";
 lister[1] = "element 2";
 lister[2] = "element 3";
 lister[3] = "element 4";

 function OnGUI()
 {
     List(Rect(50, 150, 150, 50), 150, "Choose one", lister);
 }

I've seen several attempts online and the unify javascript example doesn't work so is there a way to send multiple variables back or pass by reference the Boolean? Thanks!