source balloon.tcl
button .b -text Go -command Hello
set_balloon .b {Press for a new window}
button .e -text Quit -command exit
set_balloon .e {Exit this program}
pack .b .e -side left
proc Hello {} {
  catch {destroy .hi}
  toplevel .hi
  button .hi.b -text {Hello, World!} -command {destroy .hi}
  set_balloon .hi.b {Make this window disappear}
  pack .hi.b
}