Via a macro, define an Elixir Function with Arity of Provided Arguments

elixir-varargs-macro.ex

# tags: #code-golf
# Define a method like this:
# `VarArgs.def(:hi, [:there, :world])
# You get a function:
# `def hi(there, world) ...`
defmodule VarArgs do
  defmacro def(name, args) do
    params = Enum.map(args, fn(a) -> Macro.var(a, nil) end)
    quote do
      def unquote(:"#{name}")(unquote_splicing(params)) do
        arg_values = Enum.join(unquote(params), ", ")
        IO.puts "You called #{unquote(name)}(#{arg_values})"
        IO.puts "Params:"
        Enum.each((0..length(unquote(params)) - 1), fn(n) ->
          IO.puts "#{Enum.at(unquote(args), n)}: #{Enum.at(unquote(params), n)}"
        end)
      end
    end
  end
end

defmodule Client do
  require VarArgs

  VarArgs.def("foo", [:bar, :baz])
end

Client.foo(42, 13)
# You called foo(42, 13)
# Params:
# bar: 42
# baz: 13