I'm probably misunderstanding the question, but after reading this post 
I wrote a quick ruby test script to see if I could increment a variable 
using a tkbutton and it seemed to work for me.  Here is the code I used. 
(I don't know if this is what you are trying to do though)

require 'tk'

class Hi
  @var = 1;

  @b1 = TkButton.new(:text => "Click me", :command => proc {puts @var; 
@var += 1}).pack


  def initialize
    Tk.mainloop
  end
end

h = Hi.new()


############the first batch of code I wrote didn't have a class 
definition, I changed it so I could see what it would look like inside 
of a class, here is the original code

require 'tk'

var = 1;

b1 = TkButton.new(:text => "Click me", :command => proc {puts var; var 
+= 1}).pack

Tk.mainloop


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