Flattening an Array in ReasonML

I needed to flatten an array of arrays the other day, and couldn't find any great examples upon a quick search. Here's how to flatten an array in Reason!

let flattenArray = (arr: array(array('a))): array('a) =>
  Array.(concat(to_list(arr)));

Here is the OCaml equivalent:

let flattenArray arr = Array.(concat (to_list arr))