doctor_translate.erl

-module(doctor_translate).
-export([loop/0, watch/0]).

%Assignments:
%Make the Doctor process restart itself if it should die. 
%+
%Make a monitor for the Doctor monitor. If either monitor dies, restart it.

loop() ->
  process_flag(trap_exit, true),
  receive
    new ->
      io:format("Creating and monitoring process.~n"),
      register(translator, spawn_link(fun translate_service:loop/0)),
      loop();
    {'EXIT', From, Reason} ->
      io:format("The translate service ~p died with reason ~p.~n", [From, Reason]),
      io:format("Restarting... ~n"),
      self() ! new,
      loop()
end.

watch() ->
  process_flag(trap_exit, true),
  receive
    new ->
      io:format("Creating and monitoring new Doctor process.~n"),
      register(doctor, spawn_link(fun loop/0)),
      doctor ! new,
      watch();
    {'EXIT', From, Reason} ->
      io:format("The translate service doctor ~p died with reason ~p.~n", [From, Reason]),
      io:format("Restarting... ~n"),
      self() ! new,
      watch()
end.

translate_service.erl

% Based on: https://media.pragprog.com/titles/btlang/code/erlang/translate_service.erl
-module(translate_service).
-export([loop/0, translate/2]).

%Assignment: Monitor the translate_service and restart it should it die.
loop() ->
    receive
        {From, "casa"} -> 
            From ! "house", 
            loop();
        {From, "blanca"} -> 
            From ! "white", 
            loop();
        {From, _} -> 
            From ! "I don't understand.", 
            exit("Undefined word.")       
    end.

translate(To, Word) ->
    To ! {self(), Word}, 
    receive
        Translation -> Translation
    end.

Usage.md

Usage

c(translate_service).
c(doctor_translate).

Doctor = spawn(fun doctor_translate:watch/0).
Doctor ! new.

translate_service:translate(translator, "casa").
translate_service:translate(translator, "blanca").
translate_service:translate(translator, "incorrect").
translate_service:translate(translator, "casa").