Dialyzer Magic

analyze_test.erl

%% @doc If you run dyalizer on this module it will complain saying
%%      <pre>analyze_test.erl:11: The variable _ can never match since previous clauses completely covered the type []</pre>
%%      It took me a while to figure out what it was doing...
%%      It's not complaining that I call a function that returns [pid()] inside a function that should return [atom()].
%%      It says: "that function is fine... as long as it always return []" (which is both a list of pids and a list of atoms)
-module(analyze_test).

-export([exists/0]).

-spec list_of_atoms() -> [atom()].
-spec list_of_pids() -> [pid()].
list_of_pids() -> erlang:processes(). %% or other function that returns a (possibly empty) list of pids
list_of_atoms() -> list_of_pids().

-spec exists() -> boolean().
exists() -> case list_of_atoms() of [] -> false; _ -> true end.