Attempts to make a reason function work in JS

concat.re

[@bs.deriving jsConverter]
type args = {
  key1: option(string),
  key2: option(string),
  key3: option(string),
};

let concat = ({key1, key2, key3}) =>
  switch (key1, key2, key3) {
  | (Some(k1), Some(k2), Some(k3)) => k1 ++ ", " ++ k2 ++ ", " ++ k3
  | _ => "Something is None"
  };

let concatFromJs = [%raw {|
  ({key1, key2, key3}) => {
    const argArr = argsFromJs({key1, key2, key3})
    return concat(argArr)
   /* argsFromJs is generated by jsConverter */
  }
|}];

/* test */

Js.log(
  "call from reason: " ++ 
  concat(
    {key1: Some("value1"), key2: Some("value2"), key3: None}
  )
);

Js.log(
  "call from reason: " ++ 
  concat(
    {key1: Some("value1"), key2: Some("value2"), key3: Some("value3")}
  )
);

[%raw {|
  // optional check is fine with None
  console.log('call from js:', concatFromJs({key1: "value1", key2: "value2"}))
|}];

[%raw {|
  // optional check is not fine with Some
  console.log('call from js:', concatFromJs({key1: "value1", key2: "value2", key3: "value3"}))
|}];

/* result are below 

"call from reason: Something is None"
"call from reason: value1, value2, value3"
"call from js:" "Something is None"
"call from js:" "v, v, v" // argsFromJs is not handling option(string) from javascript correctly
*/

// so it makes really difficult to expose a function to javascript side that accepts objects possibly contains optional values

re-func.re

// exposing functions take js object with optional key

[%%raw "var john = {name: 'john', job: 'awesome job'}"];

type person = Js.t({
  .
  name: string,
  age: option(int),
  job: string
});

[@bs.val] external john : person = "john";

let p: person = [%bs.obj {
  name: "person name",
  job: "person job",
  age: None
}];

let getName = (a: person) => a##name
let getAge = (a: person) => switch (a##age) {
  | None => 0
  | Some(n) => n
}

let pn = p##name
let name = john->getName;
let age = john->getAge;

Js.log(name);
Js.log(age);

Reason-Option-Iterop-Issue.md

I wanted to make an npm module via ReasonML

• a function need to accept objects
• but couldn't find a way to convert an JS Object to a Reason Record (holds optional value)

// I wanted to have an npm module function like below
reasonFnExposedToJs({key1: 'blah', key2: undefined})

// and works fine with Reason side but generated argsFromJs looks like below
function argsFromJs(param) {
  return /* record */[
          /* key1 */param.key1,
          /* key2 */param.key2,
          /* key3 */param.key3
        ];
}
// which doesn't map possible optional values

// so end up printing only first character of string since option is implemented as [something]

I made this gist to file an issue to Reason.
Now I tried the same code with Reason online editor, and it works fine, so I think it's fixed now with new version.

found my answer with https://gist.github.com/ryuheechul/573ea3c203d8fb736ed82480cb8dafbc#file-re-func-re after playing more with reason