# When did Core remove polymorphic comparison operators in recent OCaml? **URL:** \ **Category:** Ecosystem\ **Tags:** core, base\ **Created:** [April 27, 2020, 3:21pm UTC](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633 "2020-04-27T15:21:36Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![trungta](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/trungta/32/2909_2.png) [@trungta](https://discuss.ocaml.org/u/trungta)\ **Post date:** [April 27, 2020, 3:21pm UTC](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633/1 "2020-04-27T15:21:36Z")
Hi, I’m using the Core library in a project, and recently when I upgraded my OCaml from 4.08.1 to 4.10.0, plenty of compilation errors suddenly appear for comparison expressions like: `if (xs = []) then ...` or `if (x = true) then ...` I saw that this change was discussed in this [thread](https://discuss.ocaml.org/t/monomorphic-comparison-operator-of-janestreet-base-library/1585) about monomorphic comparison operators in Base, but did not expect that Core would make it a default behavior. So I’d like to ask since which version that Core removed such polymorphic comparison operators? (I couldn’t find it in release notes of Core) Also, if I define a sum type like `type ternary = True | False | Unkn`, what will be a correct way to write `if (x = True) then ...` (which is allowed in the new Core)? I can temporarily fix by writing `if (x == True) then ...`, but using `==` doesn’t seem correct, since `==` is about comparing physical objects… Thanks for spending your time to check my question. ---
**Author:** ![bcc32](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/bcc32/32/203_2.png) [@bcc32](https://discuss.ocaml.org/u/bcc32)\ **Post date:** [April 27, 2020, 3:59pm UTC](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633/2 "2020-04-27T15:59:44Z")
The change was announced in [[ANN] v0.13 release of Jane Street packages](https://discuss.ocaml.org/t/ann-v0-13-release-of-jane-street-packages/4735), although unfortunately it doesn’t look like the CHANGES.md file was updated in the repo. I would consider the thread to be the canonical announcement. > [@trungta](#): > > Also, if I defined a sum type like `type ternary = True | False | Unkn` , what will be a correct way to write `if (x = True) then ...` (which is allowed in the new Core)? Here’s a few suggestions: 1. Define equality/compare functions using [`ppx_compare`](https://github.com/janestreet/ppx_compare) ```ocaml type ternary = True | False | Unkn [@@deriving equal] let f x = if (equal_ternary x True) then ... ``` 1. Define equality/compare functions manually ```ocaml let equal_ternary t1 t2 = match t1, t2 with | True, True | False, False | Unkn, Unkn -> true | _ -> false ``` 1. Explicitly request polymorphic comparison operators using the `Poly` module: ```ocaml let f x = if (Poly.(=) x True) then ... ``` ---
**Author:** ![trungta](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/trungta/32/2909_2.png) [@trungta](https://discuss.ocaml.org/u/trungta)\ **Post date:** [April 27, 2020, 4:15pm UTC](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633/3 "2020-04-27T16:15:59Z")
@bbc2: Thank you very much for the reference and the suggestions! 👍 ---
**Author:** ![trungta](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/trungta/32/2909_2.png) [@trungta](https://discuss.ocaml.org/u/trungta)\ **Post date:** [April 27, 2020, 5:15pm UTC](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633/4 "2020-04-27T17:15:52Z")
btw, > [@bcc32](#): > > type ternary = True | False | Unkn [@@deriving equal] should be: `[@@deriving eq]` ---
**Author:** ![bcc32](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/bcc32/32/203_2.png) [@bcc32](https://discuss.ocaml.org/u/bcc32)\ **Post date:** [April 27, 2020, 5:23pm UTC](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633/5 "2020-04-27T17:23:26Z")
> [@trungta](#): > > should be: `[@@deriving eq]` That depends on which preprocessor you are using. `[@@deriving equal]` comes from ppx\_compare, whereas `[@@deriving eq]` comes from [ppx\_deriving](https://github.com/ocaml-ppx/ppx_deriving). Base/Core and the like have better support for the former, which is a Jane Street project, although you can feel free to use the latter—the naming conventions are different, so it may not be as convenient. ---
**Author:** ![bcc32](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/bcc32/32/203_2.png) [@bcc32](https://discuss.ocaml.org/u/bcc32)\ **Post date:** [April 27, 2020, 5:42pm UTC](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633/6 "2020-04-27T17:42:29Z")
Actually, I see now that `[@@deriving eq]` defines a function called `equal_ternary`, so I guess the names do, in fact, match, so they would probably be interchangeable. ---
**Author:** ![trungta](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/trungta/32/2909_2.png) [@trungta](https://discuss.ocaml.org/u/trungta)\ **Post date:** [April 27, 2020, 5:49pm UTC](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633/7 "2020-04-27T17:49:36Z")
> [@bcc32](#): > > That depends on which preprocessor you are using. `[@@deriving equal]` comes from ppx\_compare, whereas `[@@deriving eq]` comes from [ppx\_deriving](https://github.com/ocaml-ppx/ppx_deriving). Ah, thanks for the information. I wasn’t aware that there are two `ppx` that could produce `equal`.