open Fieldglass

let sample : (string * bool, string) lens' =
  lens ~view:fst ~set:(fun value (_, other) -> value, other)

let () = assert (view sample ("colour", true) = "colour")

let () =
  let source = "colour", true in
  assert (set sample "grey" source = ("grey", true));
  assert (set sample (view sample source) source = source);
  assert (set sample "blue" (set sample "grey" source) = set sample "blue" source);
  let calls = ref 0 in
  assert (over sample ~f:(fun text -> incr calls; text ^ "s") source = ("colours", true));
  assert (!calls = 1)