Testing Purescript's Erlang Backend (https://github.com/purerl/purerl). Comparison with Caramel (https://github.com/AbstractMachinesLab/caramel) for OCaml -> Erlang conversion.

Main.purs

module Main where

import Control.Bind (bind, discard)
import Data.Function (($))
import Data.Maybe (Maybe(..))
import Data.Semigroup ((<>))
import Data.Show (show)
import Data.Unit (Unit)
import Effect (Effect)
import Effect.Class.Console (log)
import Erl.Process (SpawnedProcessState, spawn, (!))

data Msg = Reset | Add Int | Hello String

data State = State String Int

showState :: State -> String
showState (State s i) = "State (" <> show s <> ", " <> show i <> ")"

handle_message :: State -> Maybe Msg -> State
handle_message (State x y) msg =
  case msg of
    Just Reset -> State "" 0
    Just (Add z) -> State x z
    Just (Hello n) -> State n y
    Nothing -> (State x y)

loop :: forall a. State -> SpawnedProcessState (Maybe Msg) -> Effect a
loop state recv = do
  log ("current_state: " <> showState state)
  msg <- recv.receiveWithTimeout 5000 Nothing
  loop (handle_message state msg) recv

main :: Effect Unit
main = do
  p <- spawn $ loop $ State "hi" 0
  p ! (Just (Hello "joe"))

main@eps.erl

% Generated by purs version 0.0.7
-module(main@ps).
-export(['State'/0, 'Reset'/0, 'Add'/0, 'Hello'/0, showState/0, showState/1, handle_message/0, handle_message/2, loop/0, loop/2, main/0]).
-compile(nowarn_shadow_vars).
-compile(nowarn_unused_vars).
-compile(nowarn_unused_function).
-compile(no_auto_import).
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 15).
'State'() -> fun (Value0) ->
  fun (Value1) ->
    { state, Value0, Value1 }
  end
end.
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 13).
'Reset'() -> { reset }.
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 13).
'Add'() -> fun (Value0) ->
  { add, Value0 }
end.
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 13).
'Hello'() -> fun (Value0) ->
  { hello, Value0 }
end.
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 17).
showState() -> fun
  ({ state, S, I }) -> 
  (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), <<"State ("/utf8>>, (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), (data_show@ps:show((data_show@ps:showString()), S)), (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), <<", "/utf8>>, (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), (data_show@ps:show((data_show@ps:showInt()), I)), <<")"/utf8>>))))))))
end.
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 17).
showState(_@0) -> (fun
  ({ state, S, I }) -> 
  (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), <<"State ("/utf8>>, (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), (data_show@ps:show((data_show@ps:showString()), S)), (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), <<", "/utf8>>, (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), (data_show@ps:show((data_show@ps:showInt()), I)), <<")"/utf8>>))))))))
end(_@0)).
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 20).
handle_message() -> fun (V) ->
  fun (Msg) ->
    (fun
      ({ state, X, Y }, Msg1) -> 
      (fun
        ({ just, { reset } }) -> 
        { state, <<""/utf8>>, 0 };
        ({ just, { add, Z } }) -> 
        { state, X, Z };
        ({ just, { hello, N } }) -> 
        { state, N, Y };
        ({ nothing }) -> 
        { state, X, Y }
      end(Msg1))
    end(V, Msg))
  end
end.
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 20).
handle_message(_@1,_@2) -> ((fun (V) ->
  fun (Msg) ->
    (fun
      ({ state, X, Y }, Msg1) -> 
      (fun
        ({ just, { reset } }) -> 
        { state, <<""/utf8>>, 0 };
        ({ just, { add, Z } }) -> 
        { state, X, Z };
        ({ just, { hello, N } }) -> 
        { state, N, Y };
        ({ nothing }) -> 
        { state, X, Y }
      end(Msg1))
    end(V, Msg))
  end
end(_@1))(_@2)).
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 28).
loop() -> fun (State) ->
  fun (Recv) ->
    fun
      __do() -> 
      ((effect_class_console@ps:log((effect_class@ps:monadEffectEffect()), (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), <<"current_state: "/utf8>>, (main@ps:showState(State))))))()),
      Msg = ((((maps:get(receiveWithTimeout, Recv))(5000))((data_maybe@ps:'Nothing'())))()),
      ((main@ps:loop((main@ps:handle_message(State, Msg)), Recv))())
    end
  end
end.
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 28).
loop(_@3,_@4) -> fun
  __do() -> 
  ((effect_class_console@ps:log((effect_class@ps:monadEffectEffect()), (data_semigroup@ps:append((data_semigroup@ps:semigroupString()), <<"current_state: "/utf8>>, (main@ps:showState(_@3))))))()),
  Msg = ((((maps:get(receiveWithTimeout, _@4))(5000))((data_maybe@ps:'Nothing'())))()),
  ((main@ps:loop((main@ps:handle_message(_@3, Msg)), _@4))())
end.
-file("/Volumes/Dev/foss/purescript-erlang-backend-test/src/Main.purs", 34).
main() -> fun
  __do() -> 
  P = ((fun erl_process@ps:spawn/1(((main@ps:loop())({ state, <<"hi"/utf8>>, 0 }))))()),
  ((erl_process@ps:send(P, { just, { hello, <<"joe"/utf8>> } }))())
end.

OCaml.erl

% Source code generated with Caramel.
-module(holder_annotated).
-export_type([msg/0]).
-export_type([state/0]).

-export([do_work/0]).
-export([handle_message/2]).
-export([loop/2]).
-export([start/1]).

-type msg() :: reset
             | {add, integer()}
             | {hello, binary()}
             .

-type state() :: {binary(), integer()}.

-spec handle_message(state(), option:t(msg())) -> state().
handle_message(State, Msg) ->
  {X, Y} = State,
  case Msg of
    {some, reset} -> {<<"">>, 0};
    {some, {add, Z}} -> {X, Z};
    {some, {hello, N}} -> {N, Y};
    none -> State
  end.

-spec loop(fun((process:after_time()) -> option:t(msg())), state()) -> ok.
loop(Recv, State) ->
  io:format(<<"current_state: ~p\n">>, [State | []]),
  Msg = Recv({bounded, 5000}),
  State2 = handle_message(State, Msg),
  loop(Recv, State2).

-spec start(state()) -> erlang:pid(msg()).
start(X) -> process:make(fun
  (_self, Recv) -> loop(Recv, X)
end).

-spec do_work() -> ok.
do_work() ->
  Pid = start({<<"hi">>, 0}),
  erlang:send(Pid, {hello, <<"joe">>}).

OCaml.ml

type msg = [ `Reset | `Add of int | `Hello of string ]

type state = string * int

let handle_message : state -> msg option -> state =
 fun state msg ->
  let x, y = state in
  match msg with
  | Some `Reset -> ("", 0)
  | Some (`Add z) -> (x, z)
  | Some (`Hello n) -> (n, y)
  | None -> state

let rec loop ~recv state =
  Io.format "current_state: ~p\n" [ state ];
  let msg = recv ~timeout:(Process.Bounded 5000) in
  let state2 = handle_message state msg in
  loop ~recv state2

let start x = Process.make (fun _self recv -> loop ~recv x)

let do_work () =
  let pid = start ("hi", 0) in
  Erlang.send pid (`Hello "joe")