Simple circular buffers for Lua, which took me forever to get right for some reason.

buffer.lua

-- Circular buffer functionality
local Buffer = {}

function Buffer:new(ob)
  local o = ob or {}
  o.entries = #o
  o.cursor = #o + 1
  o.max = 10
  setmetatable(o, self)
  self.__index = self
  return o
end

function Buffer:append(entry)
  if self[self.cursor] then
    self[self.cursor] = entry
  else
    table.insert(self, entry)
  end
  self.cursor = self.cursor + 1
  if self.cursor == self.max + 1 then
    self.cursor = 1
  end
  if self.entries ~= self.max then
    self.entries = self.entries + 1
  end
end

function Buffer:get(idx)
  -- Allow negative indexes
  if idx < 0 then
    idx = (self.entries + idx) + 1
  end

  if self.entries == self.max then
    local c = self.cursor + idx - 1
    if c > self.max then
      c = c - self.max
    end
    return self[c]
  else
    return self[idx]
  end
end