queue.lua

Queue = class(function(q)
    q.first = 0
    q.last  = -1
  end)

function Queue.push(self, value)
  local last = self.last + 1
  self.last = last
  self[last] = value
end

function Queue.pop(self)
  local first = self.first
  if first > self.last then
    error("Queue is empty")
  end
  local ret = self[first]
  self[first] = nil
  if self.first == self.last then
    self.first = 0
    self.last = -1
  else
    self.first = first + 1
  end
  return ret
end

function Queue.peek(self)
  return self[self.first]
end

function Queue.len(self)
  return self.last - self.first + 1
end

function Queue.clear(self)
  for i=self.first,self.last do
    self[i]=nil
  end
  self.first = 0
  self.last = -1
end