Deprecate Exp.function_ in favour of Exp.function_cases going forward

ast/ast_helper_lite.ml

@@ -203,13 +203,16 @@ module Exp = struct
   let constant ?loc ?attrs a = mk ?loc ?attrs (Pexp_constant a)
   let let_ ?loc ?attrs a b c = mk ?loc ?attrs (Pexp_let (a, b, c))
 
-  let function_ ?loc ?attrs ?loc_location cases =
+  let function_cases ?loc ?attrs ?loc_location cases =
     let loc_locations =
       match loc_location with Some l -> l | None -> !default_loc
     in
     mk ?loc ?attrs
       (Pexp_function ([], None, Pfunction_cases (cases, loc_locations, [])))
 
+  (* TODO: In ppxlib 0.36.0 this should be changed to be a constructor of Pexp_function *)
+  let function_ = function_cases
+
   let fun_ ?loc ?attrs a b c d =
     let pparam_desc = Pparam_val (a, b, c) in
     let body = Pfunction_body d in

ast/ast_helper_lite.mli

@@ -150,9 +150,23 @@ module Exp : sig
     pattern ->
     expression ->
     expression
+  (** [fun lbl guard pat expr] constructs a function with arity 1. *)
 
   val function_ :
     ?loc:loc -> ?attrs:attrs -> ?loc_location:loc -> case list -> expression
+  [@@ocaml.deprecated "Use function_cases instead"]
+  (** [function_ cases] creates a new expression that represents 
+      [function c1 -> e1 | c2 -> e2 ...]. 
+     
+     @deprecated Use {! function_cases} for this behaviour. In OCaml 5.2 the AST
+     changed to represent [fun x ->] and [function ...] using the same AST node.
+     [function_] will change in the ppxlib 0.36.0 to construct this AST node.
+  *)
+
+  val function_cases :
+    ?loc:loc -> ?attrs:attrs -> ?loc_location:loc -> case list -> expression
+  (** [function_ cases] creates a new expression that represents 
+      [function c1 -> e1 | c2 -> e2 ...]. *) 
 
   val apply :
     ?loc:loc ->