TEST_GUI = function() {
  library(tcltk2)
  win1 <- tktoplevel()
  win1$env$rb1 <- tk2radiobutton(win1)
  win1$env$rb2 <- tk2radiobutton(win1)
  win1$env$rb3 <- tk2radiobutton(win1)
  rbValue <- tclVar("PANDA")

  tkconfigure(win1$env$rb1, variable = rbValue, value = 1)
  tkconfigure(win1$env$rb2, variable = rbValue, value = 2)
  tkconfigure(win1$env$rb3, variable = rbValue, value = 3)
  tkgrid(
    tk2label(win1, text = "現在要執行的功能?"),
    columnspan = 2,
    padx = 10,
    pady = c(10, 5)
  )
  tkgrid(tk2label(win1, text = "建模"),
         win1$env$rb1,
         padx = 10,
         pady = c(0, 5))
  tkgrid(tk2label(win1, text = "校正"),
         win1$env$rb2,
         padx = 10,
         pady = c(0, 5))
  tkgrid(tk2label(win1, text = "分析"),
         win1$env$rb3,
         padx = 10,
         pady = c(0, 5))

  onOK <- function() {
    rbVal <<- as.character(tclvalue(rbValue)) ###### 使用 <<- 讓 rbVal 存在於 onOK 之外而 TEST_GUI 之內
    tkdestroy(win1)
  }

  win1$env$butOK <-
    tk2button(win1,
              text = "OK",
              width = -6,
              command = onOK)
  tkgrid(
    win1$env$butOK,
    columnspan = 2,
    padx = 10,
    pady = c(5, 15)
  )
  tkfocus(win1)
  tkwait.window(win1) ###### 結束前必須先tkwait.window()
  return(rbVal)       ###### 把 rbVal 傳出去
}


a <- TEST_GUI()
str(a)