An abstract type for reading any number into an int with atdgen

rounded.ml

(*
   An atdgen type for reading any number into an int.

   `1.0` is the default output for the atd type float, which
   we want to support but is not supported by the regular parser
   for atd type int.

   `1.0` will be read as the OCaml int `1` and written back as `1`.
   
   The definition that goes into the .atd file is:
   
      type rounded <ocaml module="Rounded" t="t"> = abstract
*)

type t = int

(*
   Round a float to the nearest int
*)
let round x =
  if x > 0. then
    truncate (x +. 0.5)
  else
    truncate (x -. 0.5)

let test_round () =
  assert (round 123.45 = 123);
  assert (round 0.6 = 1);
  assert (round 0.4 = 0);
  assert (round (-0.4) = 0);
  assert (round (-0.6) = -1);
  true

let read_t ls lb =
  let x = Yojson.Basic.read_number ls lb in
  round x

let write_t ob x =
  Yojson.Basic.write_int ob x

let validate_t path x = None

This isn't pretty or convenient but gets the job done. A solution built into atdgen would be more convenient.