functools.exs

defmodule Functools do
  def reduce(func, [head|tail], acc) do
    reduce(func, tail, func.(head, acc))
  end

  def reduce(_func, [], acc) do
    acc
  end

  def map(func, [head|tail]) do
    [func.(head)|map(func, tail)]
  end

  def map(_func, []) do
    []
  end

  def filter(predicate, [head|tail]) do
    if predicate.(head) do
      [head|filter(predicate, tail)]
    else
      filter(predicate, tail)
    end
  end

  def filter(_predicate, []) do
    []
  end
end

IO.puts Functools.reduce(&+/2, [1, 2, 3], 0)
Functools.map(&IO.puts/1, [1, 2, 3])
IO.puts Functools.filter(fn x -> x != "d" end, ["d", "e", "f"])