$ erl Erlang R14B02 (erts-5.8.3) [source] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false] Eshell V5.8.3 (abort with ^G) 1> c(onion). {ok,onion} 2> onion:run(5). 5 3> onion:run(10). 55 4> -----------------------%- onion:run(N) prints Nth Fibonacci number, but it can do much more...