Support OCaml 4.08 (missing List.equal)

src/compilerlib/pb_raw_option.ml

@@ -44,7 +44,7 @@ let option_name_part_equal a b =
   | Extension_name a, Extension_name b -> String.equal a b
   | _ -> false
 
-let option_name_equal = List.equal option_name_part_equal
+let option_name_equal = Pb_util.List.equal option_name_part_equal
 let empty = []
 let add option_set option_name value = (option_name, value) :: option_set
 

src/compilerlib/pb_util.ml

@@ -136,6 +136,12 @@ module List = struct
       (match f x with
       | Some _ as r -> r
       | None -> find_map f tl)
+
+  let rec equal eq l1 l2 =
+    match l1, l2 with
+    | [], [] -> true
+    | [], _ :: _ | _ :: _, [] -> false
+    | a1 :: l1, a2 :: l2 -> eq a1 a2 && equal eq l1 l2
 end
 
 module Int_map = Map.Make (struct

src/compilerlib/pb_util.mli

@@ -84,6 +84,18 @@ module List : sig
 
   val find_opt : ('a -> bool) -> 'a list -> 'a option
   val find_map : ('a -> 'b option) -> 'a list -> 'b option
+
+  val equal : ('a -> 'a -> bool) -> 'a list -> 'a list -> bool
+  (** [equal eq [a1; ...; an] [b1; ..; bm]] holds when
+    the two input lists have the same length, and for each
+    pair of elements [ai], [bi] at the same position we have
+    [eq ai bi].
+
+    Note: the [eq] function may be called even if the
+    lists have different length. If you know your equality
+    function is costly, you may want to check {!compare_lengths}
+    first.
+*)
 end
 
 module Str_map : Map.S with type key = string