Is there an equivalent to MODULE for named functions in Elixir/ Erlang?

Question

Is there an equivalent for retrieving the name of a function just like like __MODULE__ retrieves the name of a Module in Elixir/Erlang?

Example:

defmodule Demo do
  def home_menu do
    module_name = __MODULE__
    func_name = :home_menu 
    # is there a __FUNCTION__
  end
End

EDITED

The selected answer works,

but calling the returned function name with apply/3 yields this error:

[error] %UndefinedFunctionError{arity: 4, exports: nil, function: :public_home, module: Demo, reason: nil}

I have a function :

defp public_home(u, m, msg, reset) do

end

The function in question will strictly be called within its module.

Is there a way to dynamically call a private function by name within its own module?

@OnorioCatenacci I see your point. The function in question will strictly be called within its module. is there a way to dynamically call a private function by name within its own module? — Charles Okwuagwu
– Charles Okwuagwu, Commented Nov 14, 2017 at 19:43
Are you recursively trying to call the function from within itself? In this particular case while I can see the appeal of not having to specify the function name, I'd say you should just bite the bullet and hard code it in the body of the function. — Onorio Catenacci
– Onorio Catenacci, Commented Nov 14, 2017 at 19:43
@OnorioCatenacci no. I store the previous and current function a user executes. I need to be able to use this to go back, and forward. Each method equates to a menu/page. I am trying to use apply to call the user.current or user.previous functions — Charles Okwuagwu
– Charles Okwuagwu, Commented Nov 14, 2017 at 19:47
Then what about Code.eval_string? hexdocs.pm/elixir/Code.html#eval_string/3 Would that work for what you need? — Onorio Catenacci
– Onorio Catenacci, Commented Nov 14, 2017 at 19:51

Aleksei Matiushkin · Accepted Answer · 2017-11-14 08:42:25Z

31

▶ defmodule M, do: def m, do: __ENV__.function  
▶ M.m                                                 
#⇒ {:m, 0}

Essentially, __ENV__ structure contains everything you might need.

answered Nov 14, 2017 at 8:42

Aleksei Matiushkin

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3 Comments

Charles Okwuagwu Over a year ago

i'm a bit confused about this, i am able to get the function name, but calling it with apply/3 fails: [error] %UndefinedFunctionError{arity: 4, exports: nil, function: :public_home, module: Demo, reason: nil}

Aleksei Matiushkin Over a year ago

Is it public? Did you pattern match and pass the name only?

Aleksei Matiushkin Over a year ago

Private functions are not accessible from outside.

Stratus3D · Accepted Answer · 2017-11-14 14:22:59Z

4

Yes, there is. In Erlang there are several predefined macros that should be able to provide the information you need:

% The name of the current function
?FUNCTION_NAME

% The arity of the current function (remember name alone isn't enough to identify a function in Erlang/Elixir)
?FUNCTION_ARITY 

% The file name of the current module
?FILE 

% The line number of the current line
?LINE

Source: http://erlang.org/doc/reference_manual/macros.html#id85926

answered Nov 14, 2017 at 14:22

Stratus3D

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3 Comments

Charles Okwuagwu Over a year ago

@do you know the elixir equivalent for each?

Stratus3D Over a year ago

No, but it looks like @mudasobwa's answer works in Elixir. __ENV__.function is the equivalent of {?FUNCTION_NAME, ?FUNCTION_ARITY}. This is one area where Elixir and Erlang differ quite a bit, so it's going to be hard to find something that works exactly the same between both of them.

PatNowak Over a year ago

No, it's not: groups.google.com/d/msg/elixir-lang-talk/VbGTz7rKebM/…

theartofrain · Accepted Answer · 2022-10-18 05:48:22Z

3

To add to Aleksei's answer, here is an example of a macro, f_name(), that returns just the name of the function.

So if you use it inside a function, like this:

def my_very_important_function() do
   Logger.info("#{f_name()}: about to do important things")
   Logger.info("#{f_name()}: important things, all done")
end

you will get a log statement similar to this:

my_very_important_function: about to do important things
my_very_important_function: important things, all done

Details:

Here is the definition of the macro:

defmodule Helper do
  defmacro f_name() do
    elem(__CALLER__.function, 0)
  end
end

(__CALLER__ is just like __ENV__, but it's the environment of the caller.)

And here is how the macro can be used in a module:

defmodule ImportantCodes do
  require Logger
  import Helper, only: [f_name: 0]

  def my_very_important_function() do
     Logger.info("#{f_name()}: doing very important things here")
  end
end

answered Oct 18, 2022 at 5:48

theartofrain

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1 Comment

theartofrain Nov 30, 2024 at 6:43

when you find a good answer, and then realize it's yours, from a couple of years ago. ; )

T0plomj3r · Accepted Answer · 2024-05-08 12:18:30Z

1

__ENV__.function |> elem(0)

Will result with the name of the function you are currently in.

answered May 8, 2024 at 12:18

T0plomj3r

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