Add convenience pretty printer for Either.t (added in 4.12)

Changes

@@ -86,6 +86,10 @@ Working version
   build (the Dune rules still do not generate a distributable compiler).
   (David Allsopp and Mark Shinwell, review by Gabriel Scherer)
 
+- #10242: Added convenience pretty printer for Either.t in the Format module.
+  (Oghenevwogaga Ebresafe, review by Nicolás Ojeda Bär,
+  Gabriel Scherer and Xavier Van de Woestyne)
+
 ### Other libraries:
 
 * #10084: Unix.open_process_args* functions now look up the program in the PATH.

stdlib/.depend

@@ -269,6 +269,7 @@ stdlib__Format.cmo : format.ml \
     stdlib__Queue.cmi \
     stdlib__List.cmi \
     stdlib__Int.cmi \
+    stdlib__Either.cmi \
     camlinternalFormatBasics.cmi \
     camlinternalFormat.cmi \
     stdlib__Buffer.cmi \
@@ -281,13 +282,15 @@ stdlib__Format.cmx : format.ml \
     stdlib__Queue.cmx \
     stdlib__List.cmx \
     stdlib__Int.cmx \
+    stdlib__Either.cmx \
     camlinternalFormatBasics.cmx \
     camlinternalFormat.cmx \
     stdlib__Buffer.cmx \
     stdlib__Format.cmi
 stdlib__Format.cmi : format.mli \
     stdlib.cmi \
     stdlib__Seq.cmi \
+    stdlib__Either.cmi \
     stdlib__Buffer.cmi
 stdlib__Fun.cmo : fun.ml \
     stdlib__Printexc.cmi \

stdlib/format.ml

@@ -1237,6 +1237,10 @@ let pp_print_result ~ok ~error ppf = function
 | Ok v -> ok ppf v
 | Error e -> error ppf e
 
+let pp_print_either ~left ~right ppf = function
+| Either.Left l -> left ppf l
+| Either.Right r -> right ppf r
+
  (**************************************************************)
 
 let compute_tag output tag_acc =

stdlib/format.mli

@@ -1120,6 +1120,14 @@ val pp_print_result :
 
     @since 4.08 *)
 
+val pp_print_either :
+  left:(formatter -> 'a -> unit) ->
+  right:(formatter -> 'b -> unit) -> formatter -> ('a, 'b) Either.t -> unit
+(** [pp_print_either ~left ~right ppf e] prints [e] on [ppf] using
+    [left] if [e] is [Either.Left _] and [right] if [e] is [Either.Right _].
+
+    @since 4.13 *)
+
 (** {1:fpp Formatted pretty-printing} *)
 
 (**