test.re

type point = {x: int, y: int};

let coords: list point = [];

let printCoords () => List.iter (fun c => Js.log c) coords;

let append raw =>
  Array.iter
    (
      fun data => {
        let p = {x: process data.x, y: process data.y};
        /* append p to coords */
        ()
      }
    )
    raw;



append data1;
append data2;
append data3;

printCoords ();

Oh, you can handle scope by passing a required variable in as a function argument, thus ensuring it's in scope. E.g.:

let printCoords coords => List.iter Js.log coords;

let coords = List.map (fun {x, y} => {x: process x, y: process y}) [data1, data2, data3];

let () = printCoords coords;

I know this.
I didn't asked how to rewrite this code to make it work.
I am interesting how to be with immutable vars that I need to change(

append data1;
append data2;
append data3;

printCoords ();

append data4;
append data5;

printCoords ();