Return Value of TCl/Tk window in R

Hello,
I have the TCl/Tk command 
"tkmessageBox(titel="",message="x",icon="question",type="okcancel")" in my R 
script. Now I want to perform some operation in relation to the user's 
choice, something like
"if (okpressed) xxx else yyy"
What values does this command give and how are they used?
Thank you, Richard

Richard M?ller - Am Spring 9 - D-58802 Balve-Eisborn
www.oeko-sorpe.de