[R] tkbutton command - how to know which button was clicked?

[JeeBee]

In the below code fragment, print(arg) always prints the
last element of rekeningen$rekening.
Is this because of lazy evaluation? I.e. arg is evaluated at
the time the button is pressed?
And, if so, how can I avoid this?
I tried function() {force(arg); print(arg)} but that didn't work either.

Thanks,
Jeebee.

  for(rek in seq(1,nrow(rekeningen))) {
    arg <- rekeningen$rekening[rek]

    tkgrid(tkbutton(frame.1,
      text=paste("Saldo historie", arg),
      command=function() print(arg)),
      sticky="news")
  }