ReasonML cycle dependency

Question

I'm working on a bucklescript binding to leafletjs based on this project .

With leaflet a Map has a function to add layer and a Layer has a function to add itself to a map.

This is what I would like to achieve with ReasonML :

module Map = {
    type t;
    [@bs.send] external addLayer : (t, Layer.t) => t = "addLayer";
};

module Layer = {
    type t;
    [@bs.send] external addTo : Map.t => unit = "addTo";
};

Unfortunately I get an unbound module Layer error.

How do I make the compiler aware of the type described after ?

Answer 1

Option 1: Define the types in a common module and alias them:

type map;
type layer;

module Map = {
    type t = map;
    [@bs.send] external addLayer : (t, layer) => t = "addLayer";
};

module Layer = {
    type t = layer;
    [@bs.send] external addTo : map => unit = "addTo";
};

Option 2: Make the modules mutually recursive:

module rec Map : {
    type t;
    [@bs.send] external addLayer : (t, Layer.t) => t = "addLayer";
} = {
    type t;
    [@bs.send] external addLayer : (t, Layer.t) => t = "addLayer";
}

and  Layer : {
    type t;
    [@bs.send] external addTo : Map.t => unit = "addTo";
} = {
    type t;
    [@bs.send] external addTo : Map.t => unit = "addTo";
};