Question

Long story short I am trying to replicate the Sleeping barber problem in Erlang.

In my solution I decided that for all the processes that are waiting I would put them into a list. Then, once it was that processes turn, I would take that PID off of the list.

Unfortunately when I call

length(myListOfPids).

it fails, as an example:

length([<0.46.0>]).
* 2: syntax error before: '<'

is there a way to store PID’s so that I can recall them and use them normally? i.e.

PID ! message

… just in case it matters here is the actual error I recieve when running my program:

=ERROR REPORT==== 1-Jul-2010::05:50:40 ===
Error in process <0.44.0> with exit value:
{badarg,[{erlang,length,[<0.46.0>]},{barber1,waitingRoom,2}]}

barber1 is my module, waitingRoom is the function that keeps track of which processes are waiting

Answer 1

Entering Pids by typing them does not work for me either.
Is that the only problem?

With code:

-module(test).
-export([loop/0]).

loop() ->
    receive
        {hello} ->
            io:format("Hello world!~n"),
            loop()
end.

I get:

 Eshell V5.7.5  (abort with ^G)
 1> Pid = spawn(fun test:loop/0).
 <0.35.0>
 2> L = [Pid].
 [<0.35.0>]
 3> length(L). 
 1