queueman

queueman = {}
--
function queueman.ctor()
--
    local self = {}

    local queue = { first = 0, last = -1 }

    function self.pushleft( value )
      local first = queue.first - 1
      queue.first = first
      queue[first] = value
    end

    function self.pushright( value )
      local last = queue.last + 1
      queue.last = last
      queue[last] = value
    end

    function self.popleft()
      local first = queue.first
      if first > queue.last then return nil end
      local value = queue[first]
      queue[first] = nil        -- to allow garbage collection
      queue.first = first + 1
      return value
    end

    function self.popright()
      local last = queue.last
      if queue.first > last then return nil end
      local value = queue[last]
      queue[last] = nil         -- to allow garbage collection
      queue.last = last - 1
      return value
    end

    function self.peekleft()
      local first = queue.first
      if first <= queue.last then return queue[first] end
      return nil
    end

    function self.peekright()
      local last = queue.last
      if queue.first <= last then return queue[last] end
      return nil
    end

    function self.skipleft()
      local first = queue.first
      if first <= queue.last then
        queue[first] = nil        -- to allow garbage collection
        queue.first = first + 1
      end
    end

    function self.skipright()
      local last = queue.last
      if queue.first <= last then
        queue[last] = nil         -- to allow garbage collection
        queue.last = last - 1
      end
    end

    function self.clear()
        queue = { first = 0, last = -1 }
    end

    function self.getfirst()
        return queue.first
    end

    function self.getlast()
        return queue.last
    end

    function self.list()

        local wrap, yield = coroutine.wrap, coroutine.yield

        local i, k = 1, queue.first

        local function iterator( i, k )
                  while k <= queue.last
                      do
                          yield( i, queue[k] )
                          i = i + 1
                          k = k + 1
                      end
              end

        return wrap( function() iterator( i, k ) end )

    end

    return self

end
--
setmetatable( queueman, { __call = function( _, ... ) return queueman.ctor( ... ) end } )