Abusing Elixir: JS equality

Do you find the == operator too strict? Do you often dream of two values being equal even though they are completely different types, or of maps being equal to absolutely nothing?

Thankfully, Elixir lets us un-import Kernel.==/2 and define our own.

defmodule JSEquality do
  def a == b, do: equal?(a, b) or equal?(b, a)
  def a != b, do: not __MODULE__.==(a, b)

  def a === b, do: strictly_equal?(a, b) or strictly_equal?(b, a)
  def a !== b, do: not __MODULE__.===(a, b)

  defp equal?(1, x) when x in [true, 1], do: true
  defp equal?(0, x) when x in [false, 0], do: true
  defp equal?("1", x) when x in [true, 1, "1"], do: true
  defp equal?("0", x) when x in [false, 0, "0"], do: true
  defp equal?("", x) when x in [false, 0, ""], do: true
  defp equal?(:undefined, x) when x in [nil, :undefined], do: true
  defp equal?(:Infinity, :Infinity), do: true
  defp equal?(:negative_Infinity, :negative_Infinity), do: true
  defp equal?([], x) when x in [false, 0, ""], do: true
  defp equal?([[]], x) when x in [false, 0, ""], do: true
  defp equal?([0], x) when x in [false, 0, "0"], do: true
  defp equal?([1], x) when x in [true, 1, "1"], do: true
  defp equal?(:NaN, _), do: false

  defp equal?(int, x) when is_integer(int),
    do: Kernel.==(int, x) or Kernel.==(Integer.to_string(int), x)

  defp equal?(list, _) when is_list(list), do: false
  defp equal?(map, _) when is_map(map), do: false
  defp equal?(x, x), do: true
  defp equal?(_, _), do: false

  defp strictly_equal?(list, _) when is_list(list), do: false
  defp strictly_equal?(map, _) when is_map(map), do: false
  defp strictly_equal?(:NaN, _), do: false
  defp strictly_equal?(x, x), do: true
  defp strictly_equal?(_, _), do: false
end

And, in use:

iex> import Kernel, except: [==: 2, !=: 2, ===: 2, !==: 2]
Kernel
iex> import JSEquality
JSEquality
iex> "hello" == "hello"
true
iex> "hello" == :world
false
iex> :undefined == nil
true
iex> "1" == [1]
true
iex> %{} == %{}
false
iex> false == "0"
true
iex> [] == []
false
iex> [[]] == false
true
iex> "" == 0      
true
iex> -123 == "-123"
true
iex> :NaN == :NaN
false
iex> "foo" === "foo"
true
iex> -1 === "-1"
false
iex> [] === []
false

Source