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Functional programming abstractions for Elixir (Beta release: APIs may change before 1.0)

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funx lib monoid sum.ex
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lib/monoid/sum.ex 

defmodule Funx.Monoid.Sum do

  @moduledoc """

  A Monoid implementation for sums.



  This monoid uses addition as its associative operation

  and `0` as the identity element.

  """



  @type t :: %__MODULE__{value: number()}



  defstruct value: 0

end



defimpl Funx.Monoid, for: Funx.Monoid.Sum do

  alias Funx.Monoid.Sum



  @spec empty(Sum.t()) :: Sum.t()

  def empty(_), do: %Sum{}



  @spec append(Sum.t(), Sum.t()) :: Sum.t()

  def append(%Sum{value: a}, %Sum{value: b}) do

    %Sum{value: a + b}

  end



  @spec wrap(Sum.t(), number()) :: Sum.t()

  def wrap(%Sum{}, value) when is_number(value), do: %Sum{value: value}



  @spec unwrap(Sum.t()) :: number()

  def unwrap(%Sum{value: value}) when is_number(value), do: value

end