The specific thing you’re looking for is :erlang.fun_info:
iex(1)> f = &String.capitalize/1
&String.capitalize/1
iex(2)> :erlang.fun_info(f)
[module: String, name: :capitalize, arity: 1, env: [], type: :external]
Note that it gives a possibly-unexpected result if given a capture that uses &n forms:
iex(3)> f2 = &String.starts_with?(&1, "foo")
#Function<42.39164016/1 in :erl_eval.expr/6>
iex(4)> :erlang.fun_info(f2)
[
pid: #PID<0.0.0>,
module: :erl_eval,
new_index: 42,
new_uniq: <<74, 179, 14, 23, 76, 2, 152, 184, 122, 207, 206, 42, 63, 68, 21,
64>>,
index: 42,
uniq: 39164016,
name: :"-expr/6-fun-3-",
arity: 1,
env: [
{3, %{}, {:value, &:elixir.eval_local_handler/2},
{:value, &:elixir.eval_external_handler/3}, %{},
[
{:clause, 3, [{:var, 3, :_capture@1}], [],
[
{:call, 3,
{:remote, 3, {:atom, 3, String}, {:atom, 3, :starts_with?}},
[
{:var, 3, :_capture@1},
{:bin, 3,
[{:bin_element, 3, {:string, 3, ~c"foo"}, :default, :default}]}
]}
]}
]}
],
type: :local
]