%% example
-module(my_error_module).
-export([atom_to_string/1, format_error/2]).

atom_to_string(Arg) when is_atom(Arg) ->
  atom_to_list(Arg);
atom_to_string(Arg) ->
  erlang:error(badarg,[Arg],
               [{error_info,#{ module => ?MODULE,
                               cause => #{ 1 => "should be an atom" }}}]).

format_error(Reason, [{_M,_F,_As,Info}|_]) ->
  ErrorInfo = proplists:get_value(error_info, Info, #{}),
  ErrorMap = maps:get(cause, ErrorInfo),
  ErrorMap#{ general => "optional general information",
             reason => io_lib:format("~p: ~p",[?MODULE, Reason]) }.
%% example