feat: add Complex.Kernel (#12)

* feat: add Complex.Kernel

* chore: make formatter happy

* chore: bump elixir requirement to Nx requirement

* Apply suggestions from code review

Co-authored-by: José Valim <jose.valim@gmail.com>

* Update lib/complex/kernel.ex

* chore: format

* docs: update readme

* Update lib/complex/kernel.ex

Co-authored-by: José Valim <jose.valim@gmail.com>

* Update README.md

Co-authored-by: José Valim <jose.valim@gmail.com>

Co-authored-by: José Valim <jose.valim@gmail.com>

Author: polvalente

README.md

@@ -5,18 +5,19 @@ numbers.
 
 Each complex number is represented as a structure holding the real and
 imaginary part.  There are functions for creation and manipulation of
-them.  Unfortunately since there is no operator overloading in Elixir the
-math functions (add, subtract, etc.) are implemented as add/2, sub/2, etc.
+them. Users can `use Complex.Kernel` to get operators to work on a mix
+of real and complex numbers.
 
 ## Installation
 
 Add *complex* as a dependency in your `mix.exs` file.
 
 ```elixir
 def deps do
-  [ { :complex, "~> 0.2.0" } ]
+  [{:complex, "~> 0.3.0"}]
 end
 ```
+
 After you are done, run `mix deps.get` in your shell to fetch and compile
 Complex. Start an interactive Elixir shell with `iex -S mix` and try the examples
 in the [examples section](#examples).
@@ -26,12 +27,15 @@ in the [examples section](#examples).
 Documentation for the package is available online via Hex at
 [http://hexdocs.pm/complex](http://hexdocs.pm/complex).  You can also generate
 local docs via the mix task
+
 ```elixir
 mix docs
 ```
+
 This will generate the HTML documentation and place it into the `doc` subdirectory.
 
 ## Examples
+
 ```elixir
 iex> Complex.new(3, 4)
 %Complex{im: 4.0, re: 3.0}

lib/complex/kernel.ex

@@ -0,0 +1,30 @@
+defmodule Complex.Kernel do
+  @moduledoc """
+  Provides operator overloading for Elixir operators.
+
+  When you `use Complex.Kernel`, be aware that the arithmetic operators
+  won't work in clause guards. For that you need to use the fully qualified
+  functions (i.e.: `when Kernel.+(a, b) == 1`) instead.
+  """
+
+  # This is defined as such so that Elixir 1.12 formatters don't complain
+  # and Elixir 1.13+ formatters don't remove the quotes from :"**" that
+  # would make this work in Elixir <= 1.12
+  @pow_atom String.to_atom("**")
+
+  defmacro __using__(_) do
+    operators = [{@pow_atom, 2}, +: 2, -: 2, /: 2, *: 2]
+
+    quote do
+      import Kernel, except: unquote(operators)
+      import Complex.Kernel, only: unquote(operators)
+    end
+  end
+
+  def a + b, do: Complex.add(a, b)
+  def a - b, do: Complex.subtract(a, b)
+  def a * b, do: Complex.multiply(a, b)
+  def a / b, do: Complex.divide(a, b)
+
+  def unquote(@pow_atom)(a, b), do: Complex.power(a, b)
+end

mix.exs

@@ -7,7 +7,7 @@ defmodule Complex.Mixfile do
       version: "0.3.0",
       description: description(),
       package: package(),
-      elixir: "~> 1.1",
+      elixir: "~> 1.12",
       deps: deps(),
       docs: [extras: [], before_closing_body_tag: &before_closing_body_tag/1]
     ]