gen_server_incorrect_args.erl:3: Undefined callback function handle_cast/2 (behaviour gen_server) gen_server_incorrect_args.erl:3: Undefined callback function init/1 (behaviour gen_server) gen_server_incorrect_args.erl:7: The inferred return type of handle_call/3 ({'no'} | {'ok'}) has nothing in common with {'noreply',_} | {'noreply',_,'hibernate' | 'infinity' | non_neg_integer()} | {'reply',_,_} | {'stop',_,_} | {'reply',_,_,'hibernate' | 'infinity' | non_neg_integer()} | {'stop',_,_,_}, which is the expected return type for the callback of the gen_server behaviour gen_server_incorrect_args.erl:7: The inferred type for the 2nd argument of handle_call/3 ('boo' | 'foo') is not a supertype of {pid(),_}, which is expected type for this argument in the callback of the gen_server behaviour