How does one use cached data in a functional language such as Erlang?

Question

I\'ve been reading a bit lately about functional languages. Coming from 10+ years of OO development, I\'m finding it difficult to get my head around how on earth one can poi

Answer 1

It is data which must be immutable in Erlang, not actors.

Long-lived actors normally live in a tail-recursive function, the arguments of which serve as their state and certainly can change between calls.

-module(cache).
-export([start/0, get_c/1, put_c/2, clear/1]).

start() -> register(spawn(fun () -> loop(dict:new()) end), cache).

loop(Dict) -> receive
                {get, From, Key} -> From ! {cache_result, Key, dict:fetch(Key, Dict)};
                {set, Key, Value} -> NewDict = dict:store(Key, Value, Dict),
                                     loop(NewDict);
                %% etc.
              end

put_c(Key, Value) -> cache ! {set, Key, Value}
%% etc.

When you call put_c, the actor's "state" changes even though all data involved is immutable.