When importing a function from typescript to rescript and then exporting a new
one from rescript to typescript (which uses the imported one from typescript internally) it throws the following error, (example to reproduce error is attached). By the way, I am using commonjs in package.json and bsconfig.json because I target nodejs not the browser.
Error
/home/user/sandbox/rescript/app/src/Main.bs.js:11
return MainGen.add(MainGen.add(a, b), c);
^
TypeError: MainGen.add is not a function
at add3 (/home/user/sandbox/rescript/app/src/Main.bs.js:11:30)
at Object._3 (/home/user/sandbox/rescript/app/node_modules/rescript/lib/js/curry.js:131:12)
at Object.add3 (/home/user/sandbox/rescript/app/src/Main.gen.ts:20:24)
at Object.<anonymous> (/home/user/sandbox/rescript/app/src/index.ts:9:13)
at Module._compile (node:internal/modules/cjs/loader:1101:14)
at Module.m._compile (/home/user/sandbox/rescript/app/node_modules/ts-node/src/index.ts:1310:23)
at Module._extensions..js (node:internal/modules/cjs/loader:1153:10)
at Object.require.extensions.<computed> [as .ts] (/home/user/sandbox/rescript/app/node_modules/ts-node/src/index.ts:1313:12)
at Module.load (node:internal/modules/cjs/loader:981:32)
at Function.Module._load (node:internal/modules/cjs/loader:822:12)
index.ts
import { add3 } from "./Main.gen";
export function add(a: number, b: number): number {
return a + b;
}
console.log(add3(10, 40, 1));
Main.res
@genType.import("./index")
external add: (int, int) => int = "add"
@genType
let add3 = (a: int, b: int, c: int) => {
add(add(a, b), c)
}
Main.bs.js
// Generated by ReScript, PLEASE EDIT WITH CARE
'use strict';
var MainGen = require("./Main.gen");
function add(prim0, prim1) {
return MainGen.add(prim0, prim1);
}
function add3(a, b, c) {
return MainGen.add(MainGen.add(a, b), c);
}
exports.add = add;
exports.add3 = add3;
/* ./Main.gen Not a pure module */
Main.gen.ts
/* TypeScript file generated from Main.res by genType. */
/* eslint-disable import/first */
import {add as addNotChecked} from './index';
// @ts-ignore: Implicit any on import
const Curry = require('rescript/lib/js/curry.js');
// In case of type error, check the type of 'add' in 'Main.re' and './index'.
export const addTypeChecked: (_1:number, _2:number) => number = addNotChecked;
// Export 'add' early to allow circular import from the '.bs.js' file.
export const add: unknown = addTypeChecked as (_1:number, _2:number) => number;
// tslint:disable-next-line:no-var-requires
const MainBS = require('./Main.bs');
export const add3: (a:number, b:number, c:number) => number = function (Arg1: any, Arg2: any, Arg3: any) {
const result = Curry._3(MainBS.add3, Arg1, Arg2, Arg3);
return result
};
I noted that when we reassign a function to another variable then for some reason we can not call the other one as function 
. What I mean is doing the following:
function A() => "Hello";
// calling A() at this point and any other point works as expected
const B = A;
// calling B() throws the same error -> (B is not a function)
const C = B;
// calling C() throws the same error -> (C is not a function)
this something similar to the code that Gen Type generates