List = {}

function List.new ()

    return {first = 0, last = -1}

end

function List.pushleft (list, value)

    local first = list.first - 1

    list.first = first

    list[first] = value

end

function List.pushright (list, value)

    local last = list.last + 1

    list.last = last

    list[last] = value

end

function List.popleft (list)

    local first = list.first

    if first > list.last then error("list is empty") end

    local value = list[first]

    list[first] = nil    -- to allow garbage collection

    list.first = first + 1

    return value

end

function List.popright (list)

    local last = list.last

    if list.first > last then error("list is empty") end

    local value = list[last]

    list[last] = nil     -- to allow garbage collection

    list.last = last - 1

    return value

end

list = {}

list = List.new

for i=1, 10 do

	List.pushleft(list, i)

end

value = List.popleft(list)

while value do

	print(value)

	value = List.popleft(list)

end