-module(l).
-export([loop/1,
	 rev/1,
         length/1,
	 times/3,
	 start_pong/1,
	 pong/1,
	 r/0,
	 start_pong2/1,
	 start_pong3/0,
	 pong/0,
	 version/0
	]).


%%%%%%%%% Sum it up %%%%%%%%%%%%%%%%%%%


loop(X) -> loop(X, 0).

loop(_X=0, Sum) -> Sum;
loop(X, Sum) -> loop(X-1, Sum+X).


%%%%%%%%% Reverse a list %%%%%%%%%%%%%%


rev(L) -> rev(L, []).

rev([], N) -> N;
rev([H|T], N) -> rev(T, [H] ++ N).

     
%%%%%%%%%% Length of a list %%%%%%%%%%%


length(L) -> length(L, 0).
     
length([], N) -> N;
length([_H|T], N) -> length(T, N+1).
     

%%%%%%%%%% Run Fun X tmes %%%%%%%%%%%%

times(_F, _Args, 0) -> ok;
times(F, Args, X) -> 
    F(Args),
    times(F, Args, X-1).


%%%%%%%%%% Echo message sent %%%%%%%%%


start_pong(Pid) ->
    spawn(l, pong, [Pid]).

pong(Pid) ->
    receive
        giveup ->
            io:format("Pong finished~n", []);
        {ping, Msg} ->
            io:format("pong: Received ping '~s'~n", [Msg]),
	    Pid ! {pong, Msg},
            pong(Pid);
        Msg ->
	    io:format("Unknwown message ~p, giving up", [Msg]),
	    exit(reason)
    end.

r() -> 
    receive X -> X end.

%%%%%%%%% Linked ping %%%%%%%%%%%%%%%

start_pong2(Pid) ->
    P = spawn(l, pong, [Pid]),
    link(P),
    P.

%%%%%%%%% Distributed ping %%%%%%%%%%

start_pong3() ->
    P = spawn(l, pong, []),
    register(pong, P),
    P.

pong() ->
    receive
        giveup ->
            io:format("Pong finished~n", []);
        {ping, Msg, Pid} ->
            io:format("ping: Received ping '~s' from '~p~n", [Msg, Pid]),
	    Pid ! {pong, Msg},
            pong();
        Msg ->
	    io:format("Unknwown message ~p, giving up", [Msg]),
	    exit(reason)
    end.


%%%%%%%%% Code replacement %%%%%%%%%%%%%%%

version() ->
    io:format("This is version 1").