implementation of enum methods in elixir

ownum.exs

defmodule Ownum do
  def all?([], _fun), do: true
  def all?([head | tail], fun) do
    if fun.(head) do
      all?(tail, fun)
    else
      false
    end
  end

  def each([], _fun), do: []
  def each([head|tail], fun) do
    [fun.(head) | each(tail, fun)]
  end

  def filter([], _fun), do: []
  def filter([head|tail], fun) do
    if fun.(head) do
      [head | filter(tail, fun)]
    else
      filter(tail, fun)
    end
  end

  def split(list, count) do
    do_split(list, [], count)
  end

  def do_split([], _acc, _count), do: []
  def do_split([head|tail], acc, count) do
    if length(acc) == count do
      [acc, [head|tail]]
    else
      do_split(tail, acc ++ [head], count)
    end
  end

  def flatten([]), do: []
  def flatten([h|t]), do: flatten(h) ++ flatten(t)
  def flatten(head), do: [head]

  def take(list, count) do
    split(list, count) |> hd
  end

end

ExUnit.start

defmodule OwnumTest do
  use ExUnit.Case, async: true
  alias Ownum

  def list do
    Enum.to_list 1..5
  end

  test :all? do
    assert Ownum.all?(list, &(&1 < 4)) == false
    assert Ownum.all?(list, &(&1 <= 5)) == true
  end

  test :each do
    assert Ownum.each([], fn(x) -> x end) == []
    assert Ownum.each([1, 2, 3], &(&1 * 2)) == [2,4,6]
  end

  test :filter do
    assert Ownum.filter(list, fn(x) -> rem(x, 2) == 1 end) == [1,3,5]
  end

  test :split do
    assert Ownum.split(list, 3) == [[1,2,3], [4,5]]
  end

  test :filter do
    assert Ownum.flatten([ [1], [ 2, 3, [4] ], 5, [[[6]]]]) == [1,2,3,4,5,6]
  end

  test :take do
    assert Ownum.take(list, 2) == [1,2]
  end
end