can record domain updates ocaml generalized?

i'm unequivocally amateur ocaml programmer greatfully atonement me stupid/obvious question. there's a lot locate i competence have missed documentation.

i have bottom formula that's starting feeling this:

let update_x p x =
  add_delta p;
  p.x <- x;
  modernise p

let update_y p y =
  add_delta p;
  p.y <- y;
  modernise p

let update_z p z =
  add_delta p;
  p.z <- z;
  modernise p 

the duplication starting bug me since i want something this:

let update_scalar p scalar value =
    add_delta p;
    magic_reflection (p, scalar) <- value;
    modernise p

this proceed i transform x i simply call:

update_scalar p 'x' value

this calls out "macros!" me nonetheless i don't trust ocaml macro system. else i do?