Not able to understand complex type and destructure it - reasonml - reason

Question

I use reason-apollo to fetch data from server. It returns me data of type (vscode shows me this type):
option(
Js.t(
< count : int;
rows : [ `User of
< firstName : string; id : string; lastName : string;
userName : string >
Js.t
| `Node of < id : string > Js.t ] option Js.Array.t >
)
)
I don't really understand type of "rows", and i am not able to get data from that. I tried this:
switch response##users {
| None => ReasonReact.string("none")
| Some(data) => {
data##rows |> Array.map(optionalRow => {
switch optionalRow {
| None => ReasonReact.string("none")
| Some(row) => ReasonReact.string(row##firstName);
}
});
ReasonReact.string("test");
}
};
but error is following:
This has type:
array(option(Js.t(({.. firstName: string} as 'a)))) =>
array(ReasonReact.reactElement)
But somewhere wanted:
Js.Array.t(option([ `Node({. "id": string})
| `User({. "firstName": string, "id": string,
"lastName": string, "userName": string}) ])) =>
'b
The incompatible parts:
array(option(Js.t('a)))
vs
Js.Array.t(option([ `Node({. "id": string})
| `User({. "firstName": string, "id": string,
"lastName": string, "userName": string}) ]))
(defined as
array(option([ `Node({. "id": string})
| `User({. "firstName": string, "id": string,
"lastName": string, "userName": string}) ])))
Further expanded:
Js.t('a)
vs
[ `Node({. "id": string})
| `User({. "firstName": string, "id": string, "lastName": string,
"userName": string}) ]
How can I get "firstName" from result?

Answer 1

Ahh clear, it's a plymorphic variant, here is snippet how to get the firstName.
...
switch optionalRow {
| None => ReasonReact.string("none")
| Some(row) => {
switch row {
| `User(u) => ReasonReact.string(u##firstName)
| `Node(n) => ReasonReact.string("test")
};
ReasonReact.string("test");
}
}
...