Elixir transducers

transducers.exs

defmodule Transducers do
  def map(f) do
    fn(step) ->
      fn(x, result) ->
        step.(f.(x), result)
      end
    end
  end

  def filter(pred) do
    fn(step) ->
      fn(x, result) ->
        if pred.(x) do
          step.(x, result)
        else
          result
        end
      end
    end
  end
end

defmodule MyEnum do
  def transduce(enum, init, transducer) do
    reduce(enum, init, transducer.(&append/2))
  end

  def reduce([], acc, _), do: acc

  def reduce(enum, acc, f) do
    [x | rest] = enum
    reduce(rest, f.(x, acc), f)
  end

  defp append(x, arr) do
    arr ++ [x]
  end
end

add_one = fn x -> x + 1 end
odd? = fn x -> rem(x, 2) != 0 end

transducer = fn f ->
  Transducers.map(add_one).(Transducers.filter(odd?).(f))
end

arr = [1, 2, 3, 4, 5, 6]

IO.inspect MyEnum.transduce(arr, [], transducer)