Silly experiment with a type-y syntax for Elixir method definitions. Not good for anything!

typed_elixir.ex

defmodule Lab do
  defmacro deft({name, _, [{:::, _, [argthing, {_, _, [:Integer]}]}]}, do: block) do
    quote do
      def unquote(name)(arg) when is_integer(arg) do
        var!(unquote(argthing)) = arg
        unquote(block)
      end
    end
  end

  defmacro deft({name, _, [{:::, _, [argthing, {_, _, [:String]}]}]}, do: block) do
    quote do
      def unquote(name)(arg) when is_binary(arg) do
        var!(unquote(argthing)) = arg
        unquote(block)
      end
    end
  end
end

defmodule Run do
  import Lab

  deft int_me(something :: Integer) do
    IO.puts 123 + something
  end

  deft string_me(something :: String) do
    IO.puts "hi " <> something
  end
end

Run.int_me(456)
Run.string_me("type system")
#Run.string_me(456)