OCamlin' along with @rexim

example.ml

let on f g = fun x y -> f (g x) (g y)

(* uncurry from https://thelema.github.io/batteries-included/hdoc/BatPervasives.html
   dunno if you can use that *)

(* line 15 can't be rewritten like that.
   I'm still trying to come up with another solution, but it's really different from the other two *)
 
(* line 16 *)
List.map (fun (vx, vy) -> atan2 (float_of_int vy) (float_of_int vx))
(* ...turns into... *)
List.map (uncurry (on atan2 float_of_int))
 
(* line 19 *)
List.sort (fun (_, a1) (_, a2) -> compare a1 a2)
(* ...turns into... *)
List.sort (uncurry (on compare snd))