ComputerCraft Tutorial: ex_turtle_select 0_2

-- #######################################
-- ex_turtle_select
-- (extend Turtle API program)
-- version 0.2
-- http://hevohevo.hatenablog.com/

-- #######################################
-- add new functions in Turtle API
-- turtle.select_org(n)
-- turtle.select(n)
-- turtle.getSelectedSlot()
-- turtle.selectNext()
-- turtle.selectPrev()

if turtle then
  turtle.select_org = turtle.select_org or turtle.select

  turtle.select = function(slot)
    turtle.select_org(slot)

    local func = function (x)
        slot = slot + x
        return (((slot-1) % 16)+1)
    end

    turtle.selectNext = function() return turtle.select_org(func(1)) end
    turtle.selectPrev = function() return turtle.select_org(func(-1)) end
    turtle.getSelectedSlot = function() return func(0) end

    return true
  end
  turtle.select(1)
  print("  extend API: turtle.select*")
end