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Erlang only supports fast prepends to lists while appending requires a full copy. Getting the size of a list is also a O(n) operation. This library implements a deque using two rotating lists to support fast append and prepend as well as O(1) size via an internal counter.


  • Bounded size
  • Enumerable protocol
  • Collectable protocol
  • Inspect protocol


Add it to mix.exs

defp deps do
  [{:deque, "~> 1.0"}]

Then use it like other Elixir data structures.

# Deque<[3, 2, 1]>
deque =
  |> Deque.appendleft(1)
  |> Deque.appendleft(2)
  |> Deque.appendleft(3)

# Deque<[2, 1]>
{3, deque} = Deque.popleft(deque)

# Deque<[6, 7, 8, 9, 10]>


Deque is released under the MIT License. Check LICENSE file for more information.

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