Indestructable Erlang REPL

gistfile1.erl

-module(shell).

-export([loop/0, eval_loop/0, eval/2]).

read() ->
  io:get_line("> ").

eval(String, Bindings) ->
  {ok, Tokens, _} = erl_scan:string(String),
  {ok, Parsed} = erl_parse:parse_exprs(Tokens),
  erl_eval:exprs(Parsed, Bindings).

print(Output) ->
  erlang:display(Output).

loop() ->
  EvalPid = gen_eval(),
  loop(orddict:new(), EvalPid).

loop(Bindings, EvalPid) ->
  Read = read(),
  case Read of
    "?EXIT.\n" ->
      print("goodbye!"),
      halt();
    _ ->
      EvalPid ! {self(), Read, Bindings},
      receive
        {Value, NewBindings} ->
          print(Value),
          loop(NewBindings, EvalPid);
        {'DOWN', _, process, _, _} ->
          NewEvalPid = gen_eval(),
          loop(Bindings, NewEvalPid)
      end
  end.

gen_eval() ->
  EvalPid = spawn(?MODULE, eval_loop, []),
  erlang:monitor(process, EvalPid),
  EvalPid.

eval_loop() ->
  receive
    {Pid, String, Bindings} ->
      {value, Value, NewBindings} = eval(String, Bindings),
      Pid ! {Value, NewBindings},
      eval_loop()
  end.