rescript-compiler Dynamic import support

Dynamic import support

Open bobzhang opened this issue 4 years ago • 10 comments

type xx 

type 'a promise 

external import : 
  'a  -> 
  ('a -> unit) -> 
  unit promise = "bootload" [@@bs.val]
;;  
module type LIST = module type of List  
;;
let _ : _ promise =     
    import (module List :  LIST)(fun (module List) -> 
  Js.log (List.length [1;2]);
  ()
  )

Todo:

Have a way to delay the generated requires for List
See if we can mitigate the runtime cost
Check to see how to ensure invariants enforced by bootload, e.g, it can only load a global module?

Nov 02 '19 01:11 bobzhang

Is this regarding #2765 ?

Nov 02 '19 02:11 yawaramin

@yawaramin yes, except the proposal here is more type safe?

Nov 02 '19 02:11 bobzhang

@bobzhang your approach here made me think about this a bit more and now I think we can do dynamic imports with just bs.val and bs.as (treating import as just a normal function), here's an example:

(* foo.ml *)
let x = 0

(* import.ml *)
module type FOO = sig
  val x : int
end

external foo : (_ [@bs.as "./foo.bs"]) -> (module FOO) Js.Promise.t =
  "import" [@@bs.val]

let _ = foo |> Js.Promise.then_(fun (module Foo : FOO) ->
  Foo.x |> Js.log |> Js.Promise.resolve)

This generates:

// Generated by BUCKLESCRIPT, PLEASE EDIT WITH CARE
'use strict';


import("./foo.bs").then((function (Foo) {
        return Promise.resolve((console.log(Foo.x), /* () */0));
      }));

/*  Not a pure module */

[EDIT: this is possible now thanks to the modules-as-objects change! On previous versions this would compile as Foo[/* x */ 0]]

Nov 02 '19 03:11 yawaramin

@bobzhang has there been progress on this? that'd be crucial for overall performance

Nov 23 '19 10:11 bloodyowl

@bobzhang any update? :-)

Nov 05 '20 21:11 sorenhoyer

@yawaramin your solution works fine. Can we make it little more generic, so that it works for any module.

Something like below

module type DyImpConfig = {module type T;};

module Make = (Config: DyImpConfig) => {
  [@bs.val] external importRe: string => Js.Promise.t(module Config.T) = "import";
};