Totally fair! I got the mutable version working, but figured it wouldn’t hurt to have a get and set function to play nicely with the chaining → operator.
I did get those working with:
@set external set: (t<'a>, 'a) => unit = "value"
@get external get: (t<'a>) => 'a = "value"
@send external peek: t<'a> => 'a = "peek"