Dictionary with arbitrary value types?

[tom-sherman]

I'm playing around with implementing a React-like UI library in Koka targeting the browser. To do this I need a way to create and update a dictionary with string keys and values of any type for the DOM element props.

Any ideas how I can do this?

Right now I have an extern JS file like this:

function newDict() {
  return Object.create(null);
}

function getDictValue(dict, key) {
  return dict[key];
}

function setDictValue(dict, key, value) {
  return {
    ...dict,
    [key]: value,
  };
}

And then:

module dict

extern import
  js file "dict.js"

pub type dict

pub inline extern dict : () -> dict
  js "newDict()"

pub inline extern get : (dict, string) -> any
  js "getDictValue(#1, #2)"

pub inline extern set : (dict, string, any) -> dict
  js "setDictValue(#1, #2, #3)"

But it gives me codegen errors, I assume because there is no C external defined?

/var/folders/p3/sbg5pmbn47x_p9zzc96vcn940000gp/T/.koka/v2.4.0/clang-debug/element.c:59:19: error: initializing 'kk_dict__dict' (aka 'struct kk_datatype_s') with an expression of incompatible type 'void'
    kk_dict__dict _ru_159 = kk_unsupported_external("dict/set"); /*dict/dict*/;

Is there a better way to do this?

[tom-sherman]

To try and avoid an XY problem:

I'm trying to create a type that can hold an arbitrary number of key-value pairs. The types need to be arbitrary. They're allowed to be so because JS (and the DOM) is untyped, you can set any time to any DOM property.

I currently have a struct element that models an element in the VDOM:

struct element
  kind : string
  children: list<element>
  props: x

I'm wondering how I can type/implement x.

[tom-sherman]

So I don't know how to solve the specific problem of an untyped value but modelling the problem in a different way helps here.

I can model every element type as a big enum, will report back when I have something working.