Computer Craft: Sample GUI

local termWidth, termHeight = term.getSize()
local selectedItem = 1
local onMainMenu = true

function Choice1()
 term.clear()
 term.setCursorPos(1,1)
 print("CHOICE 1")
 sleep(1)
end

function Exit()
 onMainMenu = false
end

mainMenu = {
[1] = { text = "Choice 1", handler = Choice1 },
[2] = { text = "Exit", handler = Exit }
}

function printMenu( menu )
 for i=1,#menu do
  if i == selectedItem then
   print(">> "..menu[i].text)
  else
   print("   "..menu[i].text)
  end
 end
end

function onKeyPressed( key, menu )
 if key == keys.enter then
  onItemSelected(menu)
 elseif key == keys.up then
  if selectedItem > 1 then
   selectedItem = selectedItem - 1
  end
 elseif key == keys.down then
  if selectedItem < #menu then
   selectedItem = selectedItem + 1
  end
 end
end

function onItemSelected( menu )
 menu[selectedItem].handler()
end

function main()
 while onMainMenu do
  term.clear()
  term.setCursorPos(1,1)
  printMenu(mainMenu)
  event, key = os.pullEvent("key")
  onKeyPressed(key,mainMenu)
 end
end

main()