Erlang toy program to sort a list of positive numbers using the sleep sort algorithm.

sleep.erl

-module( sleep ).
-export( [ sort/1, sleep/2, listen/2 ] ).

sort( Ns ) ->
    sort( Ns, 0 ).

% spawn a sleep process for each number, then start listening
sort( [], Count ) ->
    listen( Count, [] );
sort( [ N | Ns ], Count ) when is_integer( N ), N > 0 ->
    spawn( sleep, sleep, [ N, self() ] ),
    sort( Ns, Count + 1 ).

% sleep proportionally to Num, then send it back to the original process
sleep( Num, Pid ) ->
    timer:sleep( 10 * Num ),
    Pid ! Num.

% receive Count numbers back and put them in a list
listen( 0, Ns ) ->
    lists:reverse( Ns );
listen( Count, Ns ) ->
    receive
        N -> listen( Count - 1, [ N | Ns ] )
    end.