make Ast_builder.{e,p}list able to build lists such as a :: b :: c

Signed-off-by: Valentin Gatien-Baron <[email protected]>

src/ast_builder.ml

@@ -127,21 +127,29 @@ module Default = struct
   let econstruct cd arg =
     pexp_construct ~loc:cd.pcd_loc (Located.map_lident cd.pcd_name) arg
 
-  let rec elist ~loc l =
+  let rec elist ~loc ?tail l =
     match l with
-    | [] -> pexp_construct ~loc (Located.mk ~loc (Longident.Lident "[]")) None
+    | [] -> (
+        match tail with
+        | Some e -> e
+        | None ->
+            pexp_construct ~loc (Located.mk ~loc (Longident.Lident "[]")) None)
     | x :: l ->
         pexp_construct ~loc
           (Located.mk ~loc (Longident.Lident "::"))
-          (Some (pexp_tuple ~loc [ x; elist ~loc l ]))
+          (Some (pexp_tuple ~loc [ x; elist ~loc ?tail l ]))
 
-  let rec plist ~loc l =
+  let rec plist ~loc ?tail l =
     match l with
-    | [] -> ppat_construct ~loc (Located.mk ~loc (Longident.Lident "[]")) None
+    | [] -> (
+        match tail with
+        | Some p -> p
+        | None ->
+            ppat_construct ~loc (Located.mk ~loc (Longident.Lident "[]")) None)
     | x :: l ->
         ppat_construct ~loc
           (Located.mk ~loc (Longident.Lident "::"))
-          (Some (ppat_tuple ~loc [ x; plist ~loc l ]))
+          (Some (ppat_tuple ~loc [ x; plist ~loc ?tail l ]))
 
   let unapplied_type_constr_conv_without_apply ~loc (ident : Longident.t) ~f =
     match ident with
@@ -386,8 +394,8 @@ end) : S = struct
   let eapply e el = Default.eapply ~loc e el
   let eabstract ps e = Default.eabstract ~loc ps e
   let esequence el = Default.esequence ~loc el
-  let elist l = Default.elist ~loc l
-  let plist l = Default.plist ~loc l
+  let elist ?tail l = Default.elist ~loc ?tail l
+  let plist ?tail l = Default.plist ~loc ?tail l
 
   let type_constr_conv ident ~f args =
     Default.type_constr_conv ~loc ident ~f args

src/ast_builder_intf.ml

@@ -42,8 +42,8 @@ module type Additional_helpers = sig
   val pexp_tuple_opt : (expression list -> expression option) with_loc
   val pconstruct : constructor_declaration -> pattern option -> pattern
   val econstruct : constructor_declaration -> expression option -> expression
-  val elist : (expression list -> expression) with_loc
-  val plist : (pattern list -> pattern) with_loc
+  val elist : (?tail:expression -> expression list -> expression) with_loc
+  val plist : (?tail:pattern -> pattern list -> pattern) with_loc
 
   val pstr_value_list :
     loc:Location.t ->