Highlighted paste from http://pastebin.ca/1969638

p2pphonebook.erl

-module(p2pphonebook).
-export([start/1, add/2, list_all/1, update/2,delete/2,find/2,join/2,join/3,splitContacts/2,updateContactsAndPeers/2]).

%% Interface

start(X) -> spawn(fun() -> loop({dict:new(),{'','',erlang:md5(X),''}}) end).

add(Pid, Contact) ->
    rpc(Pid, {add, Contact}).

list_all(Pid) ->
    rpc(Pid, list_all).

update(Pid, Contact) ->
    rpc(Pid, {update, Contact}).

delete(Pid,Contact) ->
    rpc(Pid, {delete, Contact}).

find(Pid,ContactName) ->
    rpc(Pid, {find, ContactName}).

join(NewPeerPid, NetworkPid) ->
    rpc(NewPeerPid, {initiatejoin, NetworkPid}).

join(NetworkPid,NewPeerId,GUID) ->
    rpc(NetworkPid,{join, NewPeerId,GUID}).

updateContactsAndPeers(Pid, PeerInfo) ->
    io:format("1 ~p~p~n",[Pid,PeerInfo]),rpc(Pid,{updateInfo, PeerInfo}).

%% Internal implementation

rpc(Pid, Request) ->
    io:format("2 ~p~p~p~n",[Pid,self(),Request]), Pid ! {self(), Request},
    receive
	{Pid, Response} ->
	    io:format("3 ~p~p~p~n",[self(),Pid,Response]),Response
		
    end.

loop(ContactsAndRoutingInfo) ->
    receive
	{From, Request} ->
	    {Res, Updated} = handle_request(Request, ContactsAndRoutingInfo),
	    io:format("In loop ~p~p~p~p~p~n",[From,self(),Request,Res,Updated]),
	    From ! {self(), Res},
	    loop(Updated)
    end.

splitContacts(AtGUID, Contacts) ->
    ToHigh = fun(Name,_Contact) ->
		     erlang:md5(Name) >= AtGUID
	     end,
    Higher = dict:filter(ToHigh,Contacts),
    Lower = dict:filter(fun(N,C) ->
				not ToHigh(N,C) end, Contacts),
    {Lower,Higher}.

%% 
handle_request(Request, {Contacts,RoutingInfo={LeftPeerId,RightPeerId,LowerGUID,HigherGUID}}) ->
    case Request of
        {add, Contact} -> 
            {Name,_,_} = Contact,
	    NameGUID = erlang:md5(Name),
	    case NameGUID < LowerGUID of
		true when length(LeftPeerId) > 0 ->
		    add(LeftPeerId,Contact);
		false when NameGUID >= HigherGUID , length(RightPeerId) =:= 0 ->
		    add(RightPeerId,Contact);
		_ -> case dict:is_key(Name, Contacts) of 
			 false -> {ok, {dict:store(Name, Contact, Contacts),RoutingInfo}};
			 true  -> {{error, Name, is_already_there},
				   {Contacts,RoutingInfo}}
		     end
	    end;
        list_all ->
            List = dict:to_list(Contacts),
            {{ok, lists:map(fun({_, C}) -> C end, List)},
             {Contacts,RoutingInfo}};
        {update, Contact} ->
	    {Name,_,_} = Contact,
	    NameGUID = erlang:md5(Name),
	    case NameGUID < LowerGUID of
		true when length(LeftPeerId) > 0 ->
		    update(LeftPeerId,Contact);
		false when NameGUID >= HigherGUID , length(RightPeerId) =:= 0 ->
		    update(RightPeerId,Contact);
		_ -> {ok, {dict:store(Name, Contact, Contacts),RoutingInfo}}
	    end;
	{delete, Contact} ->
	    {Name,_,_} = Contact,
	    NameGUID = erlang:md5(Name),
	    case NameGUID < LowerGUID of
		true when length(LeftPeerId) > 0 ->
		    delete(LeftPeerId,Contact);
		false when NameGUID >= HigherGUID , length(RightPeerId) =:= 0 ->
		    delete(RightPeerId,Contact);
		_ -> case dict:is_key(Name,Contacts) of 
			 true -> case dict:fetch(Name,Contacts) of
				     Contact -> {ok, {dict:erase(Name,Contacts),RoutingInfo}};
				     _ -> {{error, Name, attributes_do_not_match},{Contacts,RoutingInfo}}
				 end;
			 false -> {{error, Name, is_not_there},
				   {Contacts,RoutingInfo}}
		     end
	    end;
	{find, Name} ->
	    NameGUID = erlang:md5(Name),
	    case NameGUID < LowerGUID of
		true when length(LeftPeerId) > 0 ->
		    find(LeftPeerId,Name);
		false when NameGUID >= HigherGUID , length(RightPeerId) =:= 0 ->
		    find(RightPeerId,Name);
		_ -> case dict:is_key(Name,Contacts) of
			 true -> {{ok,dict:fetch(Name,Contacts)},{Contacts,RoutingInfo}};
			 false -> {{error, Name, is_not_there},{Contacts,RoutingInfo}}
		     end
	    end;
	{initiatejoin, NetworkPeerId} -> 
	    %io:format("1 abc ~s~s~n",[NetworkPeerId,self()]),
	    join(NetworkPeerId,self(),LowerGUID);
	{join, NewPeerId, NewPeerGUID} ->
	    %io:format("1 abc ~s~s~s~n",[NewPeerId,NewPeerGUID,self()]),
	    case NewPeerGUID < LowerGUID  of
		true when length(LeftPeerId) =:= 0 ; NewPeerGUID < LowerGUID -> 
		    {Lower,Higher} = splitContacts(NewPeerGUID,Contacts), 
		    %updateContactsAndPeers(NewPeerId,{Lower,{LeftPeerId,self(),NewPeerGUID,LowerGUID}}),
		    io:format("Hee"),
		    NewPeerId ! {updateInfo,{Lower,{LeftPeerId,self(),NewPeerGUID,LowerGUID}}},
		    {ok, {Higher,NewPeerId,RightPeerId,LowerGUID,HigherGUID}};
		true when length(LeftPeerId) =/= 0 -> 
		    join(LeftPeerId,NewPeerId,NewPeerGUID);
		false when length(RightPeerId) =:= 0 ; NewPeerGUID > LowerGUID -> 
		    {Lower,Higher} = splitContacts(NewPeerGUID,Contacts), 
		    %updateContactsAndPeers(NewPeerId,{Higher,{self(),RightPeerId,NewPeerGUID,HigherGUID}}),
		    io:format("Haa"),
		    NewPeerId ! {updateInfo,{Higher,{self(),RightPeerId,NewPeerGUID,HigherGUID}}},
		    {ok, {Lower,LeftPeerId,NewPeerId,LowerGUID,NewPeerGUID}};
		false when length(RightPeerId) =/= 0 -> 
		    join(RightPeerId,NewPeerId,NewPeerGUID);
		_ -> 
		    {{error,unknown_case},{Contacts,RoutingInfo}}
	    end;
	{updateInfo, PeerInfo} ->
	    io:format("M ~n",[]),
	    {Contact,{NewLeftPeerId,NewRightPeerId,NewLowerGUID,NewHigherGUID}} = PeerInfo,
	    {ok, {Contact,{NewLeftPeerId,NewRightPeerId,NewLowerGUID,NewHigherGUID}}};
        Other ->
            {{error,unknown_request, Other},
             {Contacts,RoutingInfo}}
    end.