C[omp]ute

From: "andrew cooke" <andrew@...>

Date: Wed, 2 May 2007 13:38:17 -0400 (CLT)

Search for "unix pipe erlang" and it seems like everyone and their dog has
written code something like that below (they allows functions to be
chained together as parallel processes).

But what if my functions need to manage some state?  I have a rather large
(and useful) (quasi-)monad library.  How do I integrate that?

Andrew

PS "Response" doesn't make much sense out of context, but provides some
information for logging.

-module(chain).

-import(choopa_util, [res_info/2, res_info/3]).
-export([new_end/3, new_link/4, echo/2]).


bootstrap(Fun) ->
    Pid = spawn(fun() -> Fun(Fun) end),
    fun(Message) -> Pid ! Message end.

new_end(Response, Filter, Name) ->
    bootstrap(fun(Self) ->
                      receive
                          {data, Data} ->
                              Filter(Data),
                              Self(Self);
                          exit ->
                              res_info(Response, "Exiting ~s", [Name]);
                          Other ->
                              res_info(Response, "~s: unexpected ~p ",
                                       [Name, Other]),
                              Self(Self)
                      end
              end).

new_link(Response, Filter, Name, Next) ->
    bootstrap(fun(Self) ->
                      receive
                          {data, Data} ->
                              Next({data, Filter(Data)}),
                              Self(Self);
                          exit ->
                              Next(exit),
                              res_info(Response, "Exiting ~s", [Name]);
                          Other ->
                              res_info(Response, "~s: unexpected ~p ",
                                       [Name, Other]),
                              Self(Self)
                      end
              end).

echo(Response, Tag) ->
    fun(Message) -> res_info(Response, Tag),
                    Message
    end.