CODEWITHSUNDEEP
macroselixirmetaprogramming
Phillipp
Phillipp

Reputation: 1445

Elixir Macros: Get unquoted parameter value outside of quote

I have a macro which gets a module name as parameter and I want to call a function on that module to get some data in order to generate the quote block.

Example:

  defmacro my_macro(module) do
    data = apply(module, :config, [])

    # do something with data to generate the quote do end
  end

Obviously, this doesn't work because the parameter value is quoted. I could fetch the data inside the quote block and act accordingly but that would put the whole logic inside the module that uses my macro which is quite dirty. I want to inject as little code as possible.

Upvotes: 0

Views: 335

Answers (1)

Dogbert
Dogbert

Reputation: 222118

You can extract the module out by pattern matching with its quoted form: {:__aliases__, _, list} where list is a list of atoms which when concatenated with a dot (use Module.concat/1) produces the full module name.

defmodule A do
  defmacro my_macro({:__aliases__, _, list}) do
    module = Module.concat(list)
    module.foo()
  end
end

defmodule B do
  def foo do
    quote do
      42
    end
  end
end

defmodule C do
  import A
  IO.inspect my_macro B
end

Output:

42

Upvotes: 2

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