[SOLVED] Erlang -- How to convert a fun() object to a String

Erlang -- How to convert a fun() object to a String

Is there a straightforward way to convert an Erlang fun to a string? A call to io_lib:format only prints the function reference, e.g. something like "#Fun<erl_eval.20.67289768>". For example, I'd like to be able to do this:

1> Fun = fun() -> atom_to_list('hello world') end.
2> FunStr = fun_to_str(Fun).
"fun() -> atom_to_list('hello world') end."

I'm looking for how to implement fun_to_str. In javascript, some interpreters have a .toSource() function that can be called on any object, including functions, that print their string representation. Any info is appreciated, thanks.

Solution

First, get the environment variables for the fun (which includes the abstract code):

1> Fun = fun() -> atom_to_list('hello world') end.
#Fun<erl_eval.43.39164016>
2> {env, [{_, _, _, _, _, Abs}]} = erlang:fun_info(Fun, env).
{env,[{{1,7},
       [],
       {eval,#Fun<shell.23.46532814>},
       {value,#Fun<shell.5.46532814>},
       #{},
       [{clause,{1,10},
                [],[],
                [{call,{1,16},
                       {atom,{1,16},atom_to_list},
                       [{atom,{1,29},'hello world'}]}]}]}]}

Pretty print the abstract code using erl_pp:

3> io:format("~s~n", [erl_pp:expr({'fun', 1, {clauses, Abs}})]).
fun() ->
       atom_to_list('hello world')
end

(You have to add {'fun', 1, {clauses, ...}} around it to make it a complete Erlang expression)