🍬 An Erlang backend to the OCaml compiler

Getting started

You can bootstrap the system by running:

caramel $ make deps build

It relies on opam being installed, and make deps will take care of
installing all the necessary opam dependencies.

After make you should have a caramelc binary to play around with.


The target make watch will start the Dune build watcher, and recompile the
project as you save files.

You can run tests with make test, and reformat the source code with make fmt.

For a more in-depth description of what’s happening, check the the OCaml to
document, and the Caramel arch


You can find several examples in ./examples, and in

In the examples, you can run caramelc compile *.ml to get them all built in
the right order.

Here’s an OCaml module and the compiled Erlang module:

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: ~pn" [ 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")
% Source code generated with Caramel.


-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

-spec loop(fun((process: after_time()) -> option: t(msg())), state()) -> ok.
loop(Recv, State) ->
  io: format(<<"current_state: ~pn">>, [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)

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

Running on the Erlang shell we get this output:

examples/processes λ erl
Erlang/OTP 23 [erts-11.0.3] [source] [64-bit] [smp:64:64] [ds:64:64:10] [async-threads:1] [hipe]

Eshell V11.0.3  (abort with ^G)
1> c(holder_annotated).
2> holder_annotated:
do_work/0         handle_message/2  loop/2            module_info/0
module_info/1     start/1
2> holder_annotated: do_work().
current_state: {<<"hi">>,0}
current_state: {<<"joe">>,0}
current_state: {<<"joe">>,0}
BREAK: (a)bort (A)bort with dump (c)ontinue (p)roc info (i)nfo
       (l)oaded (v)ersion (k)ill (D)b-tables (d)istribution

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