I’m not sure you need a lib and a macro for this. You can get the same thing with something like this (untested):

defmodule Foo do
  for {code, message} <- {400 => "Bad Request", 401 => "Unauthorized", 403 => "Forbidden"} do
    def get(unquote(code)), do: {:ok, unquote(message)}
  end
  def get(_), do: :error
end

I occasionally use this technique.

Well, there can be some performance advantages in functional heads vs just looking things up in a map. This is more or less the way unicode support is implemented in Elixir core.

I think I’d like this more if it did not use the Map get as the function name and I’d really like it a lot more if it wasn’t called Defmap. The function is really just get_constant, or even just constant or attribute. It’s a generic tool for exposing module attributes as functions. Map is just a convenient way to structure the input, you aren’t defining a Map in any practical sense at all.

The only thing wrong with this is actually the hardest part of programming, naming stuff. I think what it does is useful.

Ah that’s cool.