CCEither(cleanup): conditionnally use the Either module

Include the Either module when available (ocaml >= 4.12)

Author: FardaleM

src/core/CCEither.ml

@@ -5,6 +5,12 @@ type 'a equal = 'a -> 'a -> bool
 type 'a ord = 'a -> 'a -> int
 type 'a printer = Format.formatter -> 'a -> unit
 
+[@@@ifge 4.12]
+
+include Either
+
+[@@@else_]
+
 (** {2 Basics} *)
 
 type ('a, 'b) t = ('a, 'b) Either.t =
@@ -62,6 +68,8 @@ let compare ~left ~right e1 e2 =
   | Left l1, Left l2 -> left l1 l2
   | Right r1, Right r2 -> right r1 r2
 
+[@@@endif]
+
 (** {2 IO} *)
 
 let pp ~left ~right fmt = function

src/core/CCEither.mli

@@ -13,6 +13,13 @@ type 'a equal = 'a -> 'a -> bool
 type 'a ord = 'a -> 'a -> int
 type 'a printer = Format.formatter -> 'a -> unit
 
+[@@@ifge 4.12]
+
+include module type of Either
+(** @inline *)
+
+[@@@else_]
+
 (** {2 Basics} *)
 
 type ('a, 'b) t = ('a, 'b) Either.t =
@@ -70,6 +77,8 @@ val compare :
   ('a, 'b) t ->
   int
 
+[@@@endif]
+
 (** {2 IO} *)
 
 val pp : left:'a printer -> right:'b printer -> ('a, 'b) t printer