diff --git a/compiler/compileArg.ml b/compiler/compileArg.ml
index 605d0ac53d..540707cdd5 100644
--- a/compiler/compileArg.ml
+++ b/compiler/compileArg.ml
@@ -17,8 +17,8 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
+open! Js_of_ocaml_compiler.Stdlib
 open Js_of_ocaml_compiler
-open Js_of_ocaml_compiler.Stdlib
 open Cmdliner
 
 type t =
@@ -248,7 +248,7 @@ let options =
       else None
     in
     let source_map =
-      if source_map <> None && not Source_map_io.enabled
+      if Option.is_some source_map && not Source_map_io.enabled
       then (
         warn
           "Warning: '--source-map' flag ignored because js_of_ocaml was compiled \
diff --git a/compiler/js_of_ocaml.ml b/compiler/js_of_ocaml.ml
index bcf62e14f0..b0d3778edd 100644
--- a/compiler/js_of_ocaml.ml
+++ b/compiler/js_of_ocaml.ml
@@ -18,8 +18,8 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
+open! Js_of_ocaml_compiler.Stdlib
 open Js_of_ocaml_compiler
-open Js_of_ocaml_compiler.Stdlib
 
 let times = Debug.find "times"
 
@@ -133,14 +133,16 @@ let f
   in
   if times () then Format.eprintf "Start parsing...@.";
   let need_debug =
-    if source_map <> None || Config.Flag.debuginfo () || toplevel
+    if Option.is_some source_map || Config.Flag.debuginfo () || toplevel
     then `Full
     else if Config.Flag.pretty ()
     then `Names
     else `No
   in
   let check_debug debug =
-    if (not runtime_only) && source_map <> None && Parse_bytecode.Debug.is_empty debug
+    if (not runtime_only)
+       && Option.is_some source_map
+       && Parse_bytecode.Debug.is_empty debug
     then
       warn
         "Warning: '--source-map' is enabled but the bytecode program was compiled with \
@@ -260,7 +262,7 @@ let f
           | (`Stdout, _), false -> `Stdout
           | (`Name x, _), false -> `Name x
           | (`Name x, true), true
-            when String.length x > 0 && x.[String.length x - 1] = '/' ->
+            when String.length x > 0 && Char.equal x.[String.length x - 1] '/' ->
               `Name (gen_unit_filename x cmo)
           | (`Name _, true), true | (`Stdout, true), true ->
               failwith "use [-o dirname/] or remove [--keep-unit-names]"
@@ -277,8 +279,8 @@ let f
               match output_file with
               | `Stdout, false -> `Name (gen_unit_filename "./" cmo)
               | `Name x, false -> `Name (gen_unit_filename (Filename.dirname x) cmo)
-              | `Name x, true when String.length x > 0 && x.[String.length x - 1] = '/'
-                ->
+              | `Name x, true
+                when String.length x > 0 && Char.equal x.[String.length x - 1] '/' ->
                   `Name (gen_unit_filename x cmo)
               | `Stdout, true | `Name _, true ->
                   failwith "use [-o dirname/] or remove [--keep-unit-names]"
diff --git a/compiler/jsoo_link.ml b/compiler/jsoo_link.ml
index fe3ab27867..00a30fe33f 100644
--- a/compiler/jsoo_link.ml
+++ b/compiler/jsoo_link.ml
@@ -17,6 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
+open! Js_of_ocaml_compiler.Stdlib
 open Js_of_ocaml_compiler
 
 let f {LinkerArg.output_file; source_map; resolve_sourcemap_url; js_files} =
diff --git a/compiler/jsoo_minify.ml b/compiler/jsoo_minify.ml
index 40e512bf96..a25ada4051 100644
--- a/compiler/jsoo_minify.ml
+++ b/compiler/jsoo_minify.ml
@@ -17,8 +17,8 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
+open! Js_of_ocaml_compiler.Stdlib
 open Js_of_ocaml_compiler
-open Js_of_ocaml_compiler.Stdlib
 
 let error k = Format.ksprintf (fun s -> failwith s) k
 
diff --git a/compiler/lib/base64.ml b/compiler/lib/base64.ml
index bec7b68cfe..5d99b74515 100644
--- a/compiler/lib/base64.ml
+++ b/compiler/lib/base64.ml
@@ -19,6 +19,8 @@
  *
  *)
 
+open! Stdlib
+
 type ('a, 'b) result =
   | Ok of 'a
   | Error of 'b
@@ -51,9 +53,9 @@ let make_alphabet alphabet =
   if String.length alphabet <> 64 then invalid_arg "Length of alphabet must be 64";
   if String.contains alphabet '='
   then invalid_arg "Alphabet can not contain padding character";
-  let emap = Array.init (String.length alphabet) (fun i -> Char.code alphabet.[i]) in
+  let emap = Array.init (String.length alphabet) ~f:(fun i -> Char.code alphabet.[i]) in
   let dmap = Array.make 256 none in
-  String.iteri (fun idx chr -> dmap.(Char.code chr) <- idx) alphabet;
+  String.iteri ~f:(fun idx chr -> dmap.(Char.code chr) <- idx) alphabet;
   {emap; dmap}
 
 let length_alphabet {emap; _} = Array.length emap
@@ -146,7 +148,7 @@ let encode_sub pad {emap; _} ?(off = 0) ?len input =
 
 let encode ?(pad = true) ?(alphabet = default_alphabet) ?off ?len input =
   match encode_sub pad alphabet ?off ?len input with
-  | Ok (res, off, len) -> Ok (String.sub res off len)
+  | Ok (res, off, len) -> Ok (String.sub res ~pos:off ~len)
   | Error _ as err -> err
 
 let encode_string ?pad ?alphabet input =
@@ -284,7 +286,7 @@ let decode_sub ?(pad = true) {dmap; _} ?(off = 0) ?len input =
 
 let decode ?pad ?(alphabet = default_alphabet) ?off ?len input =
   match decode_sub ?pad alphabet ?off ?len input with
-  | Ok (res, off, len) -> Ok (String.sub res off len)
+  | Ok (res, off, len) -> Ok (String.sub res ~pos:off ~len)
   | Error _ as err -> err
 
 let decode_sub ?pad ?(alphabet = default_alphabet) ?off ?len input =
diff --git a/compiler/lib/build_path_prefix_map.ml b/compiler/lib/build_path_prefix_map.ml
index 0803f56873..7d1c139a25 100644
--- a/compiler/lib/build_path_prefix_map.ml
+++ b/compiler/lib/build_path_prefix_map.ml
@@ -13,7 +13,7 @@
 (*                                                                        *)
 (**************************************************************************)
 
-open Stdlib
+open! Stdlib
 
 type path = string
 
@@ -107,11 +107,7 @@ let decode_map str =
 let rewrite_opt prefix_map path =
   let is_prefix = function
     | None -> false
-    | Some {target = _; source} ->
-        String.length source <= String.length path
-        && Stdlib.String.equal
-             source
-             (String.sub path ~pos:0 ~len:(String.length source))
+    | Some {target = _; source} -> String.is_prefix path ~prefix:source
   in
   match
     List.find
diff --git a/compiler/lib/code.ml b/compiler/lib/code.ml
index 259dc5f4f0..8709346429 100644
--- a/compiler/lib/code.ml
+++ b/compiler/lib/code.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 
 module Addr = struct
   type t = int
@@ -57,6 +57,8 @@ module Var : sig
 
   val print : Format.formatter -> t -> unit
 
+  val equal : t -> t -> bool
+
   val idx : t -> int
 
   val of_idx : int -> t
@@ -128,7 +130,9 @@ end = struct
   module T = struct
     type t = int
 
-    let compare v1 v2 = v1 - v2
+    let compare : t -> t -> int = compare
+
+    let equal (a : t) (b : t) = a = b
   end
 
   include T
@@ -564,9 +568,9 @@ let eq (pc1, blocks1, _) (pc2, blocks2, _) =
          &&
          try
            let block2 = Addr.Map.find pc blocks2 in
-           block1.params = block2.params
-           && block1.branch = block2.branch
-           && block1.body = block2.body
+           Poly.(block1.params = block2.params)
+           && Poly.(block1.branch = block2.branch)
+           && Poly.(block1.body = block2.body)
          with Not_found -> false)
        blocks1
        true
@@ -586,7 +590,7 @@ let invariant (_, blocks, _) =
     let define x =
       if check_defs
       then (
-        assert (defs.(Var.idx x) = false);
+        assert (not defs.(Var.idx x));
         defs.(Var.idx x) <- true)
     in
     let check_expr = function
diff --git a/compiler/lib/code.mli b/compiler/lib/code.mli
index 8b851c6ee2..c143f1a0c2 100644
--- a/compiler/lib/code.mli
+++ b/compiler/lib/code.mli
@@ -50,6 +50,8 @@ module Var : sig
 
   val print : Format.formatter -> t -> unit
 
+  val equal : t -> t -> bool
+
   val idx : t -> int
 
   val of_idx : int -> t
diff --git a/compiler/lib/config.ml b/compiler/lib/config.ml
index 0d80309f90..446e97e991 100644
--- a/compiler/lib/config.ml
+++ b/compiler/lib/config.ml
@@ -17,7 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *)
 
-open Stdlib
+open! Stdlib
 
 module Flag = struct
   let optims = ref []
@@ -137,7 +137,8 @@ module Param = struct
 
   let tc_default = TcTrampoline
 
-  let _tc_all = tc_default :: List.filter [TcNone; TcTrampoline] ~f:(( <> ) tc_default)
+  let _tc_all =
+    tc_default :: List.filter [TcNone; TcTrampoline] ~f:(Poly.( <> ) tc_default)
 
   let tailcall_optim =
     p
diff --git a/compiler/lib/constant.ml b/compiler/lib/constant.ml
index c31126a502..0215be841c 100644
--- a/compiler/lib/constant.ml
+++ b/compiler/lib/constant.ml
@@ -16,6 +16,8 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *)
 
+open! Stdlib
+
 let global_object = "joo_global_object"
 
 let extra_js_files = ["+graphics.js"; "+toplevel.js"; "+nat.js"; "+dynlink.js"]
diff --git a/compiler/lib/control.ml b/compiler/lib/control.ml
index 5e33690d92..d37bef0d3b 100644
--- a/compiler/lib/control.ml
+++ b/compiler/lib/control.ml
@@ -21,7 +21,7 @@
 (*
 FIX: is there a way to merge this with dead code elimination?
 *)
-
+open! Stdlib
 open Code
 
 (****)
diff --git a/compiler/lib/deadcode.ml b/compiler/lib/deadcode.ml
index 179ac12e09..6b68125580 100644
--- a/compiler/lib/deadcode.ml
+++ b/compiler/lib/deadcode.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 
 let debug = Debug.find "deadcode"
 
diff --git a/compiler/lib/debug.ml b/compiler/lib/debug.ml
index 679ea3ced5..52f1bc3996 100644
--- a/compiler/lib/debug.ml
+++ b/compiler/lib/debug.ml
@@ -16,7 +16,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 
 let series = ref None
 
@@ -55,7 +55,7 @@ let find s =
       state
   in
   fun () ->
-    if s = "times" then take_snapshot ();
+    if String.equal s "times" then take_snapshot ();
     (not !quiet) && !state
 
 let enable s =
diff --git a/compiler/lib/dgraph.ml b/compiler/lib/dgraph.ml
index bf6f1c6eb7..77ad673cba 100644
--- a/compiler/lib/dgraph.ml
+++ b/compiler/lib/dgraph.ml
@@ -17,6 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
+open! Stdlib
 
 module Make (N : sig
   type t
@@ -187,7 +188,7 @@ struct
   let invert size g =
     let h = NTbl.make size [] in
     NSet.iter (fun x -> g.iter_children (fun y -> add_edge h y x) x) g.domain;
-    {domain = g.domain; iter_children = (fun f x -> List.iter f (successors h x))}
+    {domain = g.domain; iter_children = (fun f x -> List.iter ~f (successors h x))}
 
   module type DOMAIN = sig
     type t
diff --git a/compiler/lib/driver.ml b/compiler/lib/driver.ml
index a7f8ad0f37..65388241b2 100644
--- a/compiler/lib/driver.ml
+++ b/compiler/lib/driver.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 
 let debug = Debug.find "main"
 
diff --git a/compiler/lib/eval.ml b/compiler/lib/eval.ml
index d57f40230c..6e1be41357 100644
--- a/compiler/lib/eval.ml
+++ b/compiler/lib/eval.ml
@@ -17,7 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 open Code
 open Flow
 
@@ -75,12 +75,12 @@ let bool b = Some (Int (if b then 1l else 0l))
 
 let eval_prim x =
   match x with
-  | Not, [Int i] -> bool (i = 0l)
-  | Lt, [Int i; Int j] -> bool (i < j)
-  | Le, [Int i; Int j] -> bool (i <= j)
-  | Eq, [Int i; Int j] -> bool (i = j)
-  | Neq, [Int i; Int j] -> bool (i <> j)
-  | Ult, [Int i; Int j] -> bool (j < 0l || i < j)
+  | Not, [Int i] -> bool Int32.(i = 0l)
+  | Lt, [Int i; Int j] -> bool Int32.(i < j)
+  | Le, [Int i; Int j] -> bool Int32.(i <= j)
+  | Eq, [Int i; Int j] -> bool Int32.(i = j)
+  | Neq, [Int i; Int j] -> bool Int32.(i <> j)
+  | Ult, [Int i; Int j] -> bool (Int32.(j < 0l) || Int32.(i < j))
   | Extern name, l -> (
       let name = Primitive.resolve name in
       match name, l with
@@ -99,12 +99,12 @@ let eval_prim x =
       | "%int_asr", _ -> shift l Int.shift_right
       | "%int_neg", [Int i] -> Some (Int (Int.neg i))
       (* float *)
-      | "caml_eq_float", _ -> float_binop_bool l ( = )
-      | "caml_neq_float", _ -> float_binop_bool l ( <> )
-      | "caml_ge_float", _ -> float_binop_bool l ( >= )
-      | "caml_le_float", _ -> float_binop_bool l ( <= )
-      | "caml_gt_float", _ -> float_binop_bool l ( > )
-      | "caml_lt_float", _ -> float_binop_bool l ( < )
+      | "caml_eq_float", _ -> float_binop_bool l Float.( = )
+      | "caml_neq_float", _ -> float_binop_bool l Float.( <> )
+      | "caml_ge_float", _ -> float_binop_bool l Float.( >= )
+      | "caml_le_float", _ -> float_binop_bool l Float.( <= )
+      | "caml_gt_float", _ -> float_binop_bool l Float.( > )
+      | "caml_lt_float", _ -> float_binop_bool l Float.( < )
       | "caml_add_float", _ -> float_binop l ( +. )
       | "caml_sub_float", _ -> float_binop l ( -. )
       | "caml_mul_float", _ -> float_binop l ( *. )
@@ -135,8 +135,8 @@ let eval_prim x =
           if Config.Flag.safe_string () && pos >= 0 && pos < String.length s
           then Some (Int (Int.of_int (Char.code s.[pos])))
           else None
-      | "caml_string_equal", [String s1; String s2] -> bool (s1 = s2)
-      | "caml_string_notequal", [String s1; String s2] -> bool (s1 <> s2)
+      | "caml_string_equal", [String s1; String s2] -> bool (String.equal s1 s2)
+      | "caml_string_notequal", [String s1; String s2] -> bool (not (String.equal s1 s2))
       | "caml_sys_getenv", [String s] -> (
         match get_static_env s with
         | Some env -> Some (String env)
@@ -161,7 +161,7 @@ let the_length_of info x =
     None
     (fun u v ->
       match u, v with
-      | Some l, Some l' when l = l' -> Some l
+      | Some l, Some l' when Int32.(l = l') -> Some l
       | _ -> None)
     x
 
@@ -195,7 +195,7 @@ let eval_instr info i =
   | Let (x, Prim (Extern ("caml_js_equals" | "caml_equal"), [y; z])) -> (
     match the_const_of info y, the_const_of info z with
     | Some e1, Some e2 ->
-        let c = if e1 = e2 then 1l else 0l in
+        let c = if Poly.(e1 = e2) then 1l else 0l in
         let c = Constant (Int c) in
         Flow.update_def info x c;
         Let (x, c)
@@ -222,7 +222,7 @@ let eval_instr info i =
     match is_int info y with
     | Unknown -> i
     | (Y | N) as b ->
-        let b = if b = N then 0l else 1l in
+        let b = if Poly.(b = N) then 0l else 1l in
         let c = Constant (Int b) in
         Flow.update_def info x c;
         Let (x, c))
@@ -299,10 +299,10 @@ let eval_branch info = function
             | 0l -> false
             (* https://github.com/ocaml/ocaml/blob/trunk/byterun/interp.c#L798 *)
             | _ -> true)
-          | CEq i -> i = j
-          | CLt i -> i < j
-          | CLe i -> i <= j
-          | CUlt i -> j < 0l || i < j
+          | CEq i -> Int32.(i = j)
+          | CLt i -> Int32.(i < j)
+          | CLe i -> Int32.(i <= j)
+          | CUlt i -> Int32.(j < 0l) || Int32.(i < j)
         in
         match res with
         | true -> Branch ftrue
@@ -371,7 +371,7 @@ let drop_exception_handler blocks =
             Addr.Set.fold
               (fun pc2 blocks ->
                 let b = Addr.Map.find pc2 blocks in
-                assert (b.handler <> parent_hander);
+                assert (Poly.(b.handler <> parent_hander));
                 let branch =
                   match b.branch with
                   | Poptrap (cont, pushtrap) ->
diff --git a/compiler/lib/findlib.ml b/compiler/lib/findlib.ml
index c8d4c82b6f..20777f1dbd 100644
--- a/compiler/lib/findlib.ml
+++ b/compiler/lib/findlib.ml
@@ -15,6 +15,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
+open! Stdlib
 
 let find_pkg_dir_ref = ref (fun _ -> raise Not_found)
 
@@ -22,10 +23,7 @@ let set_find_pkg_dir f = find_pkg_dir_ref := f
 
 let find_pkg_dir pkg = !find_pkg_dir_ref pkg
 
-let path_require_findlib path =
-  if path <> "" && path.[0] = '+'
-  then Some (String.sub path 1 (String.length path - 1))
-  else None
+let path_require_findlib path = String.drop_prefix path ~prefix:"+"
 
 let rec find_in_findlib_paths ?(pkg = "stdlib") paths name =
   match paths with
diff --git a/compiler/lib/flow.ml b/compiler/lib/flow.ml
index 1903bfc9e2..da2325206e 100644
--- a/compiler/lib/flow.ml
+++ b/compiler/lib/flow.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 
 let debug = Debug.find "flow"
 
@@ -66,7 +66,7 @@ let add_assign_def vars defs x y =
 let add_param_def vars defs x =
   add_var vars x;
   let idx = Var.idx x in
-  assert (is_undefined defs.(idx) || defs.(idx) = Param);
+  assert (is_undefined defs.(idx) || Poly.(defs.(idx) = Param));
   defs.(idx) <- Param
 
 (* x depends on y *)
@@ -275,7 +275,7 @@ let propagate2 ?(skip_param = false) defs known_origins possibly_mutable st x =
 module Domain2 = struct
   type t = bool
 
-  let equal (u : bool) v = u = v
+  let equal = Bool.equal
 
   let bot = false
 end
@@ -331,7 +331,7 @@ let the_const_of info x =
         None
         (fun u v ->
           match u, v with
-          | Some i, Some j when i = j -> u
+          | Some i, Some j when Poly.(i = j) -> u
           | _ -> None)
         x
   | Pc c -> Some c
@@ -377,7 +377,7 @@ let build_subst info vars =
       then
         let s = Var.Tbl.get info.info_known_origins x in
         if Var.Set.cardinal s = 1 then subst.(Var.idx x) <- Some (Var.Set.choose s));
-      if subst.(Var.idx x) = None then subst.(Var.idx x) <- direct_approx info x;
+      if Option.is_none subst.(Var.idx x) then subst.(Var.idx x) <- direct_approx info x;
       match subst.(Var.idx x) with
       | None -> ()
       | Some y -> Var.propagate_name x y)
diff --git a/compiler/lib/freevars.ml b/compiler/lib/freevars.ml
index 5eb1dc6109..5ea521d1ee 100644
--- a/compiler/lib/freevars.ml
+++ b/compiler/lib/freevars.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 
 let times = Debug.find "times"
 
diff --git a/compiler/lib/fs.ml b/compiler/lib/fs.ml
index a1865822e8..a7876fc403 100644
--- a/compiler/lib/fs.ml
+++ b/compiler/lib/fs.ml
@@ -15,6 +15,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
+open! Stdlib
 
 let rec find_in_path paths name =
   match paths with
@@ -24,7 +25,7 @@ let rec find_in_path paths name =
       if Sys.file_exists file then file else find_in_path rem name
 
 let find_in_path paths name =
-  if name = "" || name = "."
+  if String.is_empty name || String.equal name "."
   then raise Not_found
   else if Filename.is_relative name
   then find_in_path paths name
diff --git a/compiler/lib/generate.ml b/compiler/lib/generate.ml
index 1c7d2cb1b0..b6857d94fb 100644
--- a/compiler/lib/generate.ml
+++ b/compiler/lib/generate.ml
@@ -33,7 +33,7 @@
   - CLEAN UP!!!
 *)
 
-open Stdlib
+open! Stdlib
 
 let debug = Debug.find "gen"
 
@@ -52,7 +52,7 @@ let rec list_group_rec f g l b m n =
   | [] -> List.rev ((b, List.rev m) :: n)
   | a :: r ->
       let fa = f a in
-      if fa = b
+      if Poly.(fa = b)
       then list_group_rec f g r b (g a :: m) n
       else list_group_rec f g r fa [g a] ((b, List.rev m) :: n)
 
@@ -383,7 +383,7 @@ let access_queue queue x =
     else
       ( (elt.prop, elt.ce)
       , List.map queue ~f:(function
-            | x', elt when x = x' -> x', {elt with cardinal = pred elt.cardinal}
+            | x', elt when Var.equal x x' -> x', {elt with cardinal = pred elt.cardinal}
             | x -> x) )
   with Not_found -> (const_p, var x), queue
 
@@ -391,7 +391,7 @@ let access_queue' ~ctx queue x =
   match x with
   | Pc c ->
       let js, instrs = constant ~ctx c (Config.Param.constant_max_depth ()) in
-      assert (instrs = []);
+      assert (List.is_empty instrs);
       (* We only have simple constants here *)
       (const_p, js), queue
   | Pv x -> access_queue queue x
@@ -482,7 +482,7 @@ module DTree = struct
   let normalize a =
     a
     >> Array.to_list
-    >> List.stable_sort ~cmp:(fun (cont1, _) (cont2, _) -> compare cont1 cont2)
+    >> List.stable_sort ~cmp:(fun (cont1, _) (cont2, _) -> Poly.compare cont1 cont2)
     >> list_group fst snd
     >> List.map ~f:(fun (cont1, l1) -> cont1, List.flatten l1)
     >> List.stable_sort ~cmp:(fun (_, l1) (_, l2) ->
@@ -1088,7 +1088,9 @@ let rec translate_expr ctx queue loc _x e level : _ * J.statement_list =
                 l
                 ~init:([], mutator_p, queue)
             in
-            J.ENew (cc, if args = [] then None else Some args), or_p pc prop, queue
+            ( J.ENew (cc, if List.is_empty args then None else Some args)
+            , or_p pc prop
+            , queue )
         | Extern "caml_js_get", [Pv o; Pc (String f | IString f)] when J.is_ident f ->
             let (po, co), queue = access_queue queue o in
             J.EDot (co, f), or_p po mutable_p, queue
@@ -1139,7 +1141,7 @@ let rec translate_expr ctx queue loc _x e level : _ * J.statement_list =
             match internal_prim name with
             | Some f -> f l queue ctx loc
             | None ->
-                if name.[0] = '%'
+                if String.is_prefix name ~prefix:"%"
                 then failwith (Printf.sprintf "Unresolved internal primitive: %s" name);
                 let prim = Share.get_prim (runtime_fun ctx) name ctx.Ctx.share in
                 let prim_kind = kind (Primitive.kind name) in
@@ -1190,14 +1192,7 @@ and translate_instr ctx expr_queue loc instr =
       let keep_name x =
         match Code.Var.get_name x with
         | None -> false
-        | Some s ->
-            not
-              (String.length s >= 5
-              && s.[0] = 'j'
-              && s.[1] = 's'
-              && s.[2] = 'o'
-              && s.[3] = 'o'
-              && s.[4] = '_')
+        | Some s -> not (String.is_prefix s ~prefix:"jsoo_")
       in
       match ctx.Ctx.live.(Var.idx x), e with
       | 0, _ ->
@@ -1259,7 +1254,8 @@ and translate_instrs ctx expr_queue loc instr =
       st @ instrs, expr_queue
 
 and compile_block st queue (pc : Addr.t) frontier interm =
-  if queue <> [] && (Addr.Set.mem pc st.loops || not (Config.Flag.inline ()))
+  if (not (List.is_empty queue))
+     && (Addr.Set.mem pc st.loops || not (Config.Flag.inline ()))
   then flush_all queue (compile_block st [] pc frontier interm)
   else (
     if pc >= 0
@@ -1318,7 +1314,7 @@ and compile_block st queue (pc : Addr.t) frontier interm =
                     then false
                     else
                       let block = Addr.Map.find pc st.blocks in
-                      block.body <> []
+                      (not (List.is_empty block.body))
                       ||
                       match block.branch with
                       | Return _ -> false
@@ -1509,7 +1505,7 @@ and compile_decision_tree st _queue handler backs frontier interm succs loc cx d
           | CEq n -> J.EBin (J.EqEqEq, int32 n, cx)
           | CLt n -> J.EBin (J.Lt, int32 n, cx)
           | CUlt n ->
-              let n' = if n < 0l then unsigned (int32 n) else int32 n in
+              let n' = if Int32.(n < 0l) then unsigned (int32 n) else int32 n in
               J.EBin (J.Lt, n', unsigned cx)
           | CLe n -> J.EBin (J.Le, int32 n, cx)
         in
@@ -1677,7 +1673,7 @@ and compile_conditional st queue pc last handler backs frontier interm succs =
   res
 
 and compile_argument_passing ctx queue (pc, args) _backs continuation =
-  if args = []
+  if List.is_empty args
   then continuation queue
   else
     let block = Addr.Map.find pc ctx.Ctx.blocks in
@@ -1703,7 +1699,9 @@ and compile_exn_handling ctx queue (pc, args) handler continuation =
         in
         (* When an extra block is inserted during code generation,
          args is [] *)
-        let m = Subst.build_mapping (if args = [] then [] else block.params) args in
+        let m =
+          Subst.build_mapping (if List.is_empty args then [] else block.params) args
+        in
         let h_block = Addr.Map.find h_pc ctx.Ctx.blocks in
         let rec loop continuation old args params queue =
           match args, params with
@@ -1715,7 +1713,7 @@ and compile_exn_handling ctx queue (pc, args) handler continuation =
                 | z :: old -> Some z, old
               in
               let x' = try Some (Var.Map.find x m) with Not_found -> Some x in
-              if Var.compare x x0 = 0 || x' = z
+              if Var.compare x x0 = 0 || Option.equal Var.equal x' z
               then loop continuation old args params queue
               else
                 let (px, cx), queue = access_queue queue x in
@@ -1755,7 +1753,7 @@ and compile_branch st queue ((pc, _) as cont) handler backs frontier interm =
             in
             if debug ()
             then
-              if label = None
+              if Option.is_none label
               then Format.eprintf "continue;@ "
               else Format.eprintf "continue (%d);@ " pc;
             flush_all queue [J.Continue_statement label, J.N])
diff --git a/compiler/lib/generate_closure.ml b/compiler/lib/generate_closure.ml
index e1b121d491..5e48ea03e4 100644
--- a/compiler/lib/generate_closure.ml
+++ b/compiler/lib/generate_closure.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *)
-open Stdlib
+open! Stdlib
 open Code
 
 let debug_tc = Debug.find "gen_tc"
@@ -182,7 +182,7 @@ module Trampoline = struct
                     let free_pc = free_pc + 2 in
                     match List.rev block.body with
                     | Let (x, Apply (f, args, true)) :: rem_rev ->
-                        assert (f = ci.f_name);
+                        assert (Var.equal f ci.f_name);
                         let blocks =
                           Addr.Map.add
                             direct_call_pc
@@ -253,7 +253,7 @@ let rewrite_mutable
     rewrite_list
     {int = closures_intern; ext = closures_extern} =
   let internal_and_external = closures_intern @ closures_extern in
-  assert (closures_extern <> []);
+  assert (not (List.is_empty closures_extern));
   let all_mut, names =
     List.fold_left
       internal_and_external
@@ -270,7 +270,7 @@ let rewrite_mutable
         | _ -> assert false)
   in
   let vars = Var.Set.elements (Var.Set.diff all_mut names) in
-  if vars = []
+  if List.is_empty vars
   then free_pc, blocks, internal_and_external
   else
     match internal_and_external with
diff --git a/compiler/lib/inline.ml b/compiler/lib/inline.ml
index 28b9aa50d5..5f1fa7c100 100644
--- a/compiler/lib/inline.ml
+++ b/compiler/lib/inline.ml
@@ -18,7 +18,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 open Code
 
 let optimizable blocks pc _ =
@@ -81,7 +81,7 @@ let get_closures (_, blocks, _) =
 
 let rewrite_block (pc', handler) pc blocks =
   let block = Addr.Map.find pc blocks in
-  assert (block.handler = None);
+  assert (Option.is_none block.handler);
   let block = {block with handler} in
   let block =
     match block.branch, pc' with
@@ -128,7 +128,7 @@ let rec find_mapping mapping x =
 let simple blocks cont mapping =
   let map_var mapping x =
     let x' = find_mapping mapping x in
-    if x = x' then raise Not_found else x'
+    if Var.equal x x' then raise Not_found else x'
   in
   let map_prim_arg mapping = function
     | Pc c -> Pc c
@@ -196,7 +196,8 @@ let inline closures live_vars outer_optimizable pc (blocks, free_pc) =
                   [], (Branch (free_pc, [arg]), blocks, free_pc + 1))
             | `Exp exp -> Let (x, exp) :: rem, state
             | `Fail ->
-                if live_vars.(Var.idx f) = 1 && outer_optimizable = f_optimizable
+                if live_vars.(Var.idx f) = 1
+                   && Bool.equal outer_optimizable f_optimizable
                    (* inlining the code of an optimizable function could make
                  this code unoptimized. (wrt to Jit compilers)
                  At the moment, V8 doesn't optimize function containing try..catch.
diff --git a/compiler/lib/instr.ml b/compiler/lib/instr.ml
index fcd5268e98..4ec59917e7 100644
--- a/compiler/lib/instr.ml
+++ b/compiler/lib/instr.ml
@@ -17,6 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
+open! Stdlib
 
 type t =
   | ACC0
@@ -351,7 +352,7 @@ let ops =
      ; FIRST_UNIMPLEMENTED_OP, K_will_not_happen, "FIRST_UNIMPLEMENTED_OP" |]
   in
   let ops =
-    Array.mapi (fun i (c, k, n) -> {code = c; kind = k; name = n; opcode = i}) instrs
+    Array.mapi ~f:(fun i (c, k, n) -> {code = c; kind = k; name = n; opcode = i}) instrs
   in
   ops
 
@@ -384,5 +385,5 @@ let get_instr_exn code pc =
   let i = getu code pc in
   if i < 0 || i >= Array.length ops then raise (Bad_instruction i);
   let ins = ops.(i) in
-  if ins.kind = K_will_not_happen then raise (Bad_instruction i);
+  if Poly.(ins.kind = K_will_not_happen) then raise (Bad_instruction i);
   ins
diff --git a/compiler/lib/javascript.ml b/compiler/lib/javascript.ml
index 25a6c40a64..deb7482495 100644
--- a/compiler/lib/javascript.ml
+++ b/compiler/lib/javascript.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 
 module Num : sig
   type t
@@ -67,35 +67,36 @@ end = struct
   let of_int32 = Int32.to_string
 
   let of_float v =
-    if v = infinity
+    if Float.equal v infinity
     then "Infinity"
-    else if v = neg_infinity
+    else if Float.equal v neg_infinity
     then "-Infinity"
-    else if v <> v
+    else if not (Float.equal v v)
     then "NaN" (* [1/-0] = -inf seems to be the only way to detect -0 in JavaScript *)
-    else if v = 0. && 1. /. v = neg_infinity
+    else if Float.equal v 0. && Float.equal (1. /. v) neg_infinity
     then "-0."
     else
       let vint = int_of_float v in
-      if float_of_int vint = v
+      if Float.equal (float_of_int vint) v
       then Printf.sprintf "%d." vint
       else
         let s1 = Printf.sprintf "%.12g" v in
-        if v = float_of_string s1
+        if Float.equal v (float_of_string s1)
         then s1
         else
           let s2 = Printf.sprintf "%.15g" v in
-          if v = float_of_string s2 then s2 else Printf.sprintf "%.18g" v
+          if Float.equal v (float_of_string s2) then s2 else Printf.sprintf "%.18g" v
 
   let is_zero s = String.equal s "0"
 
   let is_one s = String.equal s "1"
 
-  let is_neg s = s.[0] = '-'
+  let is_neg s = Char.equal s.[0] '-'
 
-  let drop1 s = String.sub s ~pos:1 ~len:(String.length s - 1)
-
-  let neg s = if is_neg s then drop1 s else "-" ^ s
+  let neg s =
+    match String.drop_prefix s ~prefix:"-" with
+    | None -> "-" ^ s
+    | Some s -> s
 
   let add a b = of_int32 (Int32.add (to_int32 a) (to_int32 b))
 end
@@ -300,11 +301,10 @@ let is_ident =
   let l =
     Array.init 256 ~f:(fun i ->
         let c = Char.chr i in
-        if (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c = '_' || c = '$'
-        then 1
-        else if c >= '0' && c <= '9'
-        then 2
-        else 0)
+        match c with
+        | 'a' .. 'z' | 'A' .. 'Z' | '_' | '$' -> 1
+        | '0' .. '9' -> 2
+        | _ -> 0)
   in
   fun s ->
     (not (StringSet.mem s Reserved.keyword))
diff --git a/compiler/lib/js_assign.ml b/compiler/lib/js_assign.ml
index 28c6e8563d..dc1b10051e 100644
--- a/compiler/lib/js_assign.ml
+++ b/compiler/lib/js_assign.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 open Javascript
 
 let debug = Debug.find "shortvar"
@@ -224,14 +224,14 @@ while compiling the OCaml toplevel:
         !total;
     for i = 0 to len - 1 do
       let l = constr.(idx.(i)) in
-      if l <> [] && String.length name.(idx.(i)) = 0
+      if (not (List.is_empty l)) && String.length name.(idx.(i)) = 0
       then (
         let n = first_available l in
         let idx = idx.(i) in
         nm ~origin:idx n;
         mark_allocated l n;
         stats idx n);
-      if l = [] then assert (weight idx.(i) = 0)
+      if List.is_empty l then assert (weight idx.(i) = 0)
     done;
     if debug ()
     then (
@@ -311,18 +311,18 @@ module Preserve : Strategy = struct
           S.fold
             (fun var acc ->
               let name = names.(Var.idx var) in
-              if name <> "" then StringSet.add name acc else acc)
+              if not (String.is_empty name) then StringSet.add name acc else acc)
             (S.union state.Js_traverse.use state.Js_traverse.def)
             assigned
         in
         let _assigned =
           S.fold
             (fun var assigned ->
-              assert (names.(Var.idx var) = "");
+              assert (String.is_empty names.(Var.idx var));
               let name =
                 match Var.get_name var with
                 | Some expected_name ->
-                    assert (expected_name <> "");
+                    assert (not (String.is_empty expected_name));
                     if not (StringSet.mem expected_name assigned)
                     then expected_name
                     else
@@ -368,7 +368,7 @@ let program' (module Strategy : Strategy) p =
   let color = function
     | V v ->
         let name = names.(Var.idx v) in
-        assert (name <> "");
+        assert (not (String.is_empty name));
         ident ~var:v name
     | x -> x
   in
diff --git a/compiler/lib/js_output.ml b/compiler/lib/js_output.ml
index 20262f920c..f3115fcb19 100644
--- a/compiler/lib/js_output.ml
+++ b/compiler/lib/js_output.ml
@@ -28,7 +28,7 @@ XXX Beware automatic semi-colon insertion...
      the space cannot be replaced by a newline in the following expressions:
        e ++, e --, continue e, break e, return e, throw e
 *)
-open Stdlib
+open! Stdlib
 
 let stats = Debug.find "output"
 
@@ -290,7 +290,7 @@ struct
     for i = 0 to l - 1 do
       let c = s.[i] in
       match c with
-      | '\000' when i = l - 1 || s.[i + 1] < '0' || s.[i + 1] > '9' -> PP.string f "\\0"
+      | '\000' when i = l - 1 || not (Char.is_num s.[i + 1]) -> PP.string f "\\0"
       | '\b' -> PP.string f "\\b"
       | '\t' -> PP.string f "\\t"
       | '\n' -> PP.string f "\\n"
@@ -311,7 +311,7 @@ struct
           PP.string f (Array.unsafe_get array_conv (c lsr 4));
           PP.string f (Array.unsafe_get array_conv (c land 0xf))
       | _ ->
-          if c = quote
+          if Char.equal c quote
           then (
             PP.string f "\\";
             PP.string f (Array.unsafe_get array_str1 (Char.code c)))
@@ -378,19 +378,19 @@ struct
           PP.end_group f)
     | EStr (s, kind) ->
         let quote = best_string_quote s in
-        pp_string f ~utf:(kind = `Utf8) ~quote s
+        pp_string f ~utf:Poly.(kind = `Utf8) ~quote s
     | EBool b -> PP.string f (if b then "true" else "false")
-    | ENum s ->
-        let s = Num.to_string s in
+    | ENum num ->
+        let s = Num.to_string num in
         let need_parent =
-          if s.[0] = '-'
+          if Num.is_neg num
           then l > 13 (* Negative numbers may need to be parenthesized. *)
           else
             l = 15
             (* Parenthesize as well when followed by a dot. *)
-            && s.[0] <> 'I'
+            && (not (Char.equal s.[0] 'I'))
             (* Infinity *)
-            && s.[0] <> 'N'
+            && not (Char.equal s.[0] 'N')
           (* NaN *)
         in
         if need_parent then PP.string f "(";
@@ -443,9 +443,11 @@ struct
         then (
           PP.start_group f 1;
           PP.string f "(");
-        if op = IncrA || op = DecrA then expression 13 f e;
-        if op = IncrA || op = IncrB then PP.string f "++" else PP.string f "--";
-        if op = IncrB || op = DecrB then expression 13 f e;
+        if Poly.(op = IncrA) || Poly.(op = DecrA) then expression 13 f e;
+        if Poly.(op = IncrA) || Poly.(op = IncrB)
+        then PP.string f "++"
+        else PP.string f "--";
+        if Poly.(op = IncrB) || Poly.(op = DecrB) then expression 13 f e;
         if l > 13
         then (
           PP.string f ")";
@@ -1032,7 +1034,7 @@ struct
               output_one false x;
               loop last xs
         in
-        loop (def = None && cc' = []) cc;
+        loop (Option.is_none def && List.is_empty cc') cc;
         (match def with
         | None -> ()
         | Some def ->
@@ -1040,7 +1042,7 @@ struct
             PP.string f "default:";
             PP.break f;
             PP.start_group f 0;
-            statement_list ~skip_last_semi:(cc' = []) f def;
+            statement_list ~skip_last_semi:(List.is_empty cc') f def;
             PP.end_group f;
             PP.end_group f);
         loop true cc';
@@ -1144,12 +1146,9 @@ end
 let part_of_ident =
   let a =
     Array.init 256 ~f:(fun i ->
-        let c = Char.chr i in
-        (c >= 'a' && c <= 'z')
-        || (c >= 'A' && c <= 'Z')
-        || (c >= '0' && c <= '9')
-        || c = '_'
-        || c = '$')
+        match Char.chr i with
+        | 'a' .. 'z' | 'A' .. 'Z' | '0' .. '9' | '_' | '$' -> true
+        | _ -> false)
   in
   fun c -> Array.unsafe_get a (Char.code c)
 
@@ -1158,10 +1157,14 @@ let need_space a b =
   (part_of_ident a && part_of_ident b)
   (* do not generate end_of_line_comment.
      handle the case of "num / /* comment */ b " *)
-  || (a = '/' && b = '/')
+  ||
+  match a, b with
+  | '/', '/'
   (* https://github.com/ocsigen/js_of_ocaml/issues/507 *)
-  || (a = '-' && b = '-')
-  || (a = '+' && b = '+')
+   |'-', '-'
+   |'+', '+' ->
+      true
+  | _, _ -> false
 
 let program f ?source_map p =
   let smo =
diff --git a/compiler/lib/js_simpl.ml b/compiler/lib/js_simpl.ml
index a175d5330b..16e2a82ba7 100644
--- a/compiler/lib/js_simpl.ml
+++ b/compiler/lib/js_simpl.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-
+open! Stdlib
 module J = Javascript
 
 let rec enot_rec e =
@@ -128,8 +128,8 @@ let rec if_statement_2 e loc iftrue truestop iffalse falsestop =
       (* Generates conditional *)
       let x1, (e1, _) = assignment_of_statement iftrue in
       let x2, (e2, _) = assignment_of_statement iffalse in
-      if x1 <> x2 then raise Not_assignment;
-      let exp = if e1 = e then J.EBin (J.Or, e, e2) else J.ECond (e, e1, e2) in
+      if Poly.(x1 <> x2) then raise Not_assignment;
+      let exp = if Poly.(e1 = e) then J.EBin (J.Or, e, e2) else J.ECond (e, e1, e2) in
       [J.Variable_statement [x1, Some (exp, loc)], loc]
     with Not_assignment -> (
       try
@@ -153,9 +153,10 @@ let if_statement e loc iftrue truestop iffalse falsestop =
   let e = simplify_condition e in
   match iftrue, iffalse with
   (* Shared statements *)
-  | (J.If_statement (e', iftrue', iffalse'), loc), _ when iffalse = unopt iffalse' ->
+  | (J.If_statement (e', iftrue', iffalse'), loc), _ when Poly.(iffalse = unopt iffalse')
+    ->
       if_statement_2 (J.EBin (J.And, e, e')) loc iftrue' truestop iffalse falsestop
-  | (J.If_statement (e', iftrue', iffalse'), loc), _ when iffalse = iftrue' ->
+  | (J.If_statement (e', iftrue', iffalse'), loc), _ when Poly.(iffalse = iftrue') ->
       if_statement_2
         (J.EBin (J.And, e, J.EUn (J.Not, e')))
         loc
@@ -163,7 +164,7 @@ let if_statement e loc iftrue truestop iffalse falsestop =
         truestop
         iffalse
         falsestop
-  | _, (J.If_statement (e', iftrue', iffalse'), loc) when iftrue = iftrue' ->
+  | _, (J.If_statement (e', iftrue', iffalse'), loc) when Poly.(iftrue = iftrue') ->
       if_statement_2
         (J.EBin (J.Or, e, e'))
         loc
@@ -171,7 +172,8 @@ let if_statement e loc iftrue truestop iffalse falsestop =
         truestop
         (unopt iffalse')
         falsestop
-  | _, (J.If_statement (e', iftrue', iffalse'), loc) when iftrue = unopt iffalse' ->
+  | _, (J.If_statement (e', iftrue', iffalse'), loc) when Poly.(iftrue = unopt iffalse')
+    ->
       if_statement_2
         (J.EBin (J.Or, e, J.EUn (J.Not, e')))
         loc
@@ -187,16 +189,16 @@ let rec get_variable acc = function
   | J.ECond (e1, e2, e3) -> get_variable (get_variable (get_variable acc e1) e2) e3
   | J.EUn (_, e1) | J.EDot (e1, _) | J.ENew (e1, None) -> get_variable acc e1
   | J.ECall (e1, el, _) | J.ENew (e1, Some el) ->
-      List.fold_left get_variable acc (e1 :: el)
+      List.fold_left ~f:get_variable ~init:acc (e1 :: el)
   | J.EVar (J.V v) -> Code.Var.Set.add v acc
   | J.EVar (J.S _) -> acc
   | J.EFun _ | J.EStr _ | J.EBool _ | J.ENum _ | J.EQuote _ | J.ERegexp _ -> acc
   | J.EArr a ->
       List.fold_left
-        (fun acc i ->
+        ~f:(fun acc i ->
           match i with
           | None -> acc
           | Some e1 -> get_variable acc e1)
-        acc
+        ~init:acc
         a
-  | J.EObj l -> List.fold_left (fun acc (_, e1) -> get_variable acc e1) acc l
+  | J.EObj l -> List.fold_left ~f:(fun acc (_, e1) -> get_variable acc e1) ~init:acc l
diff --git a/compiler/lib/js_token.ml b/compiler/lib/js_token.ml
index ba60b07a55..864ca1a4ee 100644
--- a/compiler/lib/js_token.ml
+++ b/compiler/lib/js_token.ml
@@ -17,6 +17,8 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
+open! Stdlib
+
 type token =
   | T_WITH of Parse_info.t
   | T_WHILE of Parse_info.t
diff --git a/compiler/lib/js_traverse.ml b/compiler/lib/js_traverse.ml
index 92b2881043..084459d812 100644
--- a/compiler/lib/js_traverse.ml
+++ b/compiler/lib/js_traverse.ml
@@ -17,7 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 open Javascript
 
 class type mapper =
@@ -538,7 +538,7 @@ class rename_variable keeps =
             | Some (S {name; _}, block) ->
                 let v = Code.Var.fresh_n name in
                 let sub = function
-                  | S {name = name'; _} when name' = name -> V v
+                  | S {name = name'; _} when String.equal name' name -> V v
                   | x -> x
                 in
                 let s = new subst sub in
@@ -629,7 +629,7 @@ class compact_vardecl =
 
     method private pack all sources =
       let may_flush rem vars s instr =
-        if vars = []
+        if List.is_empty vars
         then rem, [], s :: instr
         else rem, [], s :: (Statement (Variable_statement (List.rev vars)), N) :: instr
       in
@@ -727,7 +727,8 @@ class clean =
                 List.rev_append l vars_rev, vars_loc, instr_rev
             | Empty_statement | Expression_statement (EVar _) ->
                 vars_rev, vars_loc, instr_rev
-            | _ when vars_rev = [] -> [], vars_loc, rev_append_st (x, loc) instr_rev
+            | _ when List.is_empty vars_rev ->
+                [], vars_loc, rev_append_st (x, loc) instr_rev
             | _ ->
                 ( []
                 , vars_loc
@@ -774,7 +775,7 @@ class clean =
         List.fold_left l ~init:([], []) ~f:(fun (st_rev, sources_rev) (x, loc) ->
             match x with
             | Statement s -> (s, loc) :: st_rev, sources_rev
-            | Function_declaration _ as x when st_rev = [] ->
+            | Function_declaration _ as x when List.is_empty st_rev ->
                 [], (m#source x, loc) :: sources_rev
             | Function_declaration _ as x ->
                 [], (m#source x, loc) :: append_st st_rev sources_rev)
@@ -807,7 +808,7 @@ let is_one = function
 
 let assign_op = function
   | exp, EBin (Plus, exp', exp'') -> (
-    match exp = exp', exp = exp'' with
+    match Poly.(exp = exp'), Poly.(exp = exp'') with
     | false, false -> None
     | true, false ->
         if is_one exp''
@@ -816,15 +817,15 @@ let assign_op = function
     | false, true ->
         if is_one exp' then Some (EUn (IncrB, exp)) else Some (EBin (PlusEq, exp, exp'))
     | true, true -> Some (EBin (StarEq, exp, ENum (Num.of_int32 2l))))
-  | exp, EBin (Minus, exp', y) when exp = exp' ->
+  | exp, EBin (Minus, exp', y) when Poly.(exp = exp') ->
       if is_one y then Some (EUn (DecrB, exp)) else Some (EBin (MinusEq, exp, y))
   | exp, EBin (Mul, exp', exp'') -> (
-    match exp = exp', exp = exp'' with
+    match Poly.(exp = exp'), Poly.(exp = exp'') with
     | false, false -> None
     | true, _ -> Some (EBin (StarEq, exp, exp''))
     | _, true -> Some (EBin (StarEq, exp, exp')))
   | exp, EBin (((Div | Mod | Lsl | Asr | Lsr | Band | Bxor | Bor) as unop), exp', y)
-    when exp = exp' ->
+    when Poly.(exp = exp') ->
       Some (EBin (translate_assign_op unop, exp, y))
   | _ -> None
 
@@ -873,7 +874,7 @@ class simpl =
               ( cond
               , (Expression_statement (EBin (Eq, v1, e1)), _)
               , Some (Expression_statement (EBin (Eq, v2, e2)), _) )
-            when v1 = v2 ->
+            when Poly.(v1 = v2) ->
               (Expression_statement (EBin (Eq, v1, ECond (cond, e1, e2))), loc) :: rem
           | Variable_statement l1 ->
               let x =
@@ -903,7 +904,7 @@ class simpl =
         List.fold_left l ~init:([], []) ~f:(fun (st_rev, sources_rev) x ->
             match x with
             | Statement s, loc -> (s, loc) :: st_rev, sources_rev
-            | (Function_declaration _ as x), loc when st_rev = [] ->
+            | (Function_declaration _ as x), loc when List.is_empty st_rev ->
                 [], (m#source x, loc) :: sources_rev
             | (Function_declaration _ as x), loc ->
                 [], (m#source x, loc) :: append_st st_rev sources_rev)
diff --git a/compiler/lib/link_js.ml b/compiler/lib/link_js.ml
index a8a234fee3..4f9298c913 100644
--- a/compiler/lib/link_js.ml
+++ b/compiler/lib/link_js.ml
@@ -16,31 +16,18 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
+open! Stdlib
 
 let sourceMappingURL = "//# sourceMappingURL="
 
 let sourceMappingURL_base64 = "//# sourceMappingURL=data:application/json;base64,"
 
-let drop_prefix ~prefix s =
-  let plen = String.length prefix in
-  if plen > String.length s
-  then None
-  else
-    try
-      for i = 0 to String.length prefix - 1 do
-        if s.[i] <> prefix.[i] then raise Exit
-      done;
-      Some (String.sub s plen (String.length s - plen))
-    with Exit -> None
-
-let _ = drop_prefix ~prefix:"qwe:" "qwe"
-
 let kind ~resolve_sourcemap_url file line =
   let s =
-    match drop_prefix ~prefix:sourceMappingURL_base64 line with
+    match String.drop_prefix ~prefix:sourceMappingURL_base64 line with
     | Some base64 -> `Json_base64 base64
     | None -> (
-      match drop_prefix ~prefix:sourceMappingURL line with
+      match String.drop_prefix ~prefix:sourceMappingURL line with
       | Some url -> `Url url
       | None -> `Other)
   in
@@ -66,7 +53,7 @@ let link ~output ~files ~resolve_sourcemap_url ~source_map =
   in
   let source_offset = ref 0 in
   List.iter
-    (fun file ->
+    ~f:(fun file ->
       let ic = open_in file in
       (try
          output_string output (Printf.sprintf "//# 1 %S" file);
diff --git a/compiler/lib/linker.ml b/compiler/lib/linker.ml
index 850c7c289c..64b63acaeb 100644
--- a/compiler/lib/linker.ml
+++ b/compiler/lib/linker.ml
@@ -18,7 +18,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 
 type fragment =
   { provides :
@@ -156,7 +156,7 @@ class check_and_warn name pi =
       let use = from#get_use_name in
       let diff = StringSet.diff def use in
       let diff = StringSet.remove name diff in
-      let diff = StringSet.filter (fun s -> String.length s <> 0 && s.[0] <> '_') diff in
+      let diff = StringSet.filter (fun s -> not (String.is_prefix s ~prefix:"_")) diff in
       if not (StringSet.is_empty diff)
       then
         warn
@@ -302,7 +302,7 @@ let add_file f =
             let rec find = function
               | [] -> None
               | (J.Function_declaration (J.S {J.name = n; _}, l, _, _), _) :: _
-                when name = n ->
+                when String.equal name n ->
                   Some (List.length l)
               | _ :: rem -> find rem
             in
diff --git a/compiler/lib/macro.ml b/compiler/lib/macro.ml
index 29de3d3c16..ade9f842eb 100644
--- a/compiler/lib/macro.ml
+++ b/compiler/lib/macro.ml
@@ -17,7 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *)
 
-open Stdlib
+open! Stdlib
 
 class macro_mapper =
   object (m)
diff --git a/compiler/lib/magic_number.ml b/compiler/lib/magic_number.ml
index eda92a2462..efa2413f6a 100644
--- a/compiler/lib/magic_number.ml
+++ b/compiler/lib/magic_number.ml
@@ -16,7 +16,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 
 type t = string * int
 
@@ -58,9 +58,11 @@ let kind (s, _) =
 let to_string (k, v) = Printf.sprintf "%s%03d" k v
 
 let compare (p1, n1) (p2, n2) =
-  if p1 <> p2 then raise Not_found;
+  if not (String.equal p1 p2) then raise Not_found;
   compare n1 n2
 
+let equal a b = compare a b = 0
+
 let current_exe =
   let v =
     match Ocaml_version.v with
diff --git a/compiler/lib/magic_number.mli b/compiler/lib/magic_number.mli
index 5bb40f8bfa..93d223c205 100644
--- a/compiler/lib/magic_number.mli
+++ b/compiler/lib/magic_number.mli
@@ -26,6 +26,8 @@ val size : int
 
 val compare : t -> t -> int
 
+val equal : t -> t -> bool
+
 val of_string : string -> t
 
 val to_string : t -> string
diff --git a/compiler/lib/mlvalue.ml b/compiler/lib/mlvalue.ml
index 8d46d0f847..2204dd7284 100644
--- a/compiler/lib/mlvalue.ml
+++ b/compiler/lib/mlvalue.ml
@@ -17,7 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 module J = Javascript
 
 let zero = J.ENum (J.Num.of_int32 0l)
diff --git a/compiler/lib/ocaml_compiler.cppo.ml b/compiler/lib/ocaml_compiler.cppo.ml
index ea36713ec6..509f235c9e 100644
--- a/compiler/lib/ocaml_compiler.cppo.ml
+++ b/compiler/lib/ocaml_compiler.cppo.ml
@@ -16,7 +16,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 
 let rec constant_of_const : _ -> Code.constant =
   let open Lambda in
@@ -50,7 +50,7 @@ let rec constant_of_const : _ -> Code.constant =
 let rec find_loc_in_summary ident' = function
   | Env.Env_empty -> None
   | Env.Env_value (_summary, ident, description)
-    when ident = ident' ->
+    when Poly.(ident = ident') ->
     Some description.Types.val_loc
   | Env.Env_value (summary,_,_)
   | Env.Env_type (summary, _, _)
@@ -85,6 +85,7 @@ let rec find_loc_in_summary ident' = function
 #if OCAML_VERSION < (4,8,0)
 (* Copied from ocaml/utils/tbl.ml *)
 module Tbl = struct
+  open Poly
   type ('a, 'b) t =
     | Empty
     | Node of ('a, 'b) t * 'a * 'b * ('a, 'b) t * int
@@ -154,7 +155,7 @@ module Symtable = struct
   module GlobalMap = struct
     type t = Ident.t numtable
 
-    let filter_global_map p gmap =
+    let filter_global_map (p : Ident.t -> bool) gmap =
       let newtbl = ref Tbl.empty in
       Tbl.iter (fun id num -> if p id then newtbl := Tbl.add id num !newtbl) gmap.num_tbl;
       {num_cnt = gmap.num_cnt; num_tbl = !newtbl}
@@ -208,7 +209,7 @@ module Symtable = struct
     module GlobalMap = Num_tbl(Ident.Map)
     include GlobalMap
 
-    let filter_global_map p (gmap : t) =
+    let filter_global_map (p : Ident.t -> bool) (gmap : t) =
       let newtbl = ref Ident.Map.empty in
       Ident.Map.iter
         (fun id num -> if p id then newtbl := Ident.Map.add id num !newtbl)
diff --git a/compiler/lib/ocaml_version.ml b/compiler/lib/ocaml_version.ml
index 0930bde1d7..e8e423ee44 100644
--- a/compiler/lib/ocaml_version.ml
+++ b/compiler/lib/ocaml_version.ml
@@ -16,7 +16,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 
 type t = int list
 
diff --git a/compiler/lib/parse_bytecode.ml b/compiler/lib/parse_bytecode.ml
index 1e9ba2ab1d..b295f70837 100644
--- a/compiler/lib/parse_bytecode.ml
+++ b/compiler/lib/parse_bytecode.ml
@@ -18,7 +18,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *)
 
-open Stdlib
+open! Stdlib
 open Code
 open Instr
 
@@ -150,7 +150,7 @@ end = struct
     let set =
       Hashtbl.fold
         (fun (_m, p) unit acc ->
-          if p = pos_fname
+          if String.equal p pos_fname
           then
             match unit.source with
             | None -> acc
@@ -362,7 +362,7 @@ end = struct
         let i : nativeint = Obj.magic x in
         let i32 = Nativeint.to_int32 i in
         let i' = Nativeint.of_int32 i32 in
-        if i' <> i then warn_overflow (Printf.sprintf "0x%nx (%nd)" i i) i32;
+        if Poly.(i' <> i) then warn_overflow (Printf.sprintf "0x%nx (%nd)" i i) i32;
         Int i32)
       else if tag = Obj.custom_tag && same_custom x 0L
       then Int64 (Obj.magic x : int64)
@@ -1042,7 +1042,7 @@ and compile infos pc state instrs =
         State.size_globals state (i + 1);
         let y = State.accu state in
         let g = State.globals state in
-        assert (g.vars.(i) = None);
+        assert (Option.is_none g.vars.(i));
         if debug_parser () then Format.printf "(global %d) = %a@." i Var.print y;
         let instrs =
           match g.override.(i) with
@@ -1410,7 +1410,7 @@ and compile infos pc state instrs =
     | CHECK_SIGNALS -> compile infos (pc + 1) state instrs
     | C_CALL1 ->
         let prim = primitive_name state (getu code (pc + 1)) in
-        if Primitive.resolve prim = "%identity"
+        if String.equal (Primitive.resolve prim) "%identity"
         then (* This is a no-op *)
           compile infos (pc + 2) state instrs
         else
@@ -1948,7 +1948,7 @@ let match_exn_traps (blocks : 'a Addr.Map.t) =
     (fun pc conts' blocks ->
       match Addr.Map.find pc blocks with
       | {branch = Pushtrap (cont1, x, cont2, conts); _} as block ->
-          assert (conts = Addr.Set.empty);
+          assert (Addr.Set.is_empty conts);
           let branch = Pushtrap (cont1, x, cont2, conts') in
           Addr.Map.add pc {block with branch} blocks
       | _ -> assert false)
@@ -1966,11 +1966,11 @@ let parse_bytecode ~debug code globals debug_data =
   let state = State.initial globals in
   Code.Var.reset ();
   let blocks =
-    Blocks.analyse (if debug = `Full then debug_data else Debug.create ()) code
+    Blocks.analyse (if Poly.(debug = `Full) then debug_data else Debug.create ()) code
   in
   let blocks =
     (* Disabled. [pc] might not be an appropriate place to split blocks *)
-    if false && debug = `Full
+    if false && Poly.(debug = `Full)
     then Debug.fold debug_data (fun pc _ blocks -> Blocks.add blocks pc) blocks
     else blocks
   in
@@ -2014,7 +2014,7 @@ let seek_section toc ic name =
   let rec seek_sec curr_ofs = function
     | [] -> raise Not_found
     | (n, len) :: rem ->
-        if n = name
+        if String.equal n name
         then (
           seek_in ic (curr_ofs - len);
           len)
@@ -2077,7 +2077,7 @@ let from_exe
       (fun id -> keep (Ident.name id))
       orig_symbols
   in
-  (if debug = `No
+  (if Poly.(debug = `No)
   then ()
   else
     try
@@ -2350,7 +2350,7 @@ let from_cmo ?(includes = [])
   seek_in ic compunit.Cmo_format.cu_pos;
   let code = Bytes.create compunit.Cmo_format.cu_codesize in
   really_input ic code 0 compunit.Cmo_format.cu_codesize;
-  if debug = `No || compunit.Cmo_format.cu_debug = 0
+  if Poly.(debug = `No) || compunit.Cmo_format.cu_debug = 0
   then ()
   else (
     seek_in ic compunit.Cmo_format.cu_debug;
@@ -2373,7 +2373,7 @@ let from_cma ?(includes = [])
         seek_in ic compunit.Cmo_format.cu_pos;
         let code = Bytes.create compunit.Cmo_format.cu_codesize in
         really_input ic code 0 compunit.Cmo_format.cu_codesize;
-        if debug = `No || compunit.Cmo_format.cu_debug = 0
+        if Poly.(debug = `No) || compunit.Cmo_format.cu_debug = 0
         then ()
         else (
           seek_in ic compunit.Cmo_format.cu_debug;
@@ -2400,14 +2400,16 @@ let from_channel ic =
   | `Pre magic -> (
     match Magic_number.kind magic with
     | `Cmo ->
-        if Config.Flag.check_magic () && magic <> Magic_number.current_cmo
+        if Config.Flag.check_magic ()
+           && not (Magic_number.equal magic Magic_number.current_cmo)
         then raise Magic_number.(Bad_magic_version magic);
         let compunit_pos = input_binary_int ic in
         seek_in ic compunit_pos;
         let compunit : Cmo_format.compilation_unit = input_value ic in
         `Cmo compunit
     | `Cma ->
-        if Config.Flag.check_magic () && magic <> Magic_number.current_cma
+        if Config.Flag.check_magic ()
+           && not (Magic_number.equal magic Magic_number.current_cma)
         then raise Magic_number.(Bad_magic_version magic);
         let pos_toc = input_binary_int ic in
         (* Go to table of contents *)
@@ -2418,7 +2420,8 @@ let from_channel ic =
   | `Post magic -> (
     match Magic_number.kind magic with
     | `Exe ->
-        if Config.Flag.check_magic () && magic <> Magic_number.current_exe
+        if Config.Flag.check_magic ()
+           && not (Magic_number.equal magic Magic_number.current_exe)
         then raise Magic_number.(Bad_magic_version magic);
         `Exe
     | _ -> raise Magic_number.(Bad_magic_number (to_string magic)))
diff --git a/compiler/lib/parse_info.ml b/compiler/lib/parse_info.ml
index 75cc1bdd0a..8597993756 100644
--- a/compiler/lib/parse_info.ml
+++ b/compiler/lib/parse_info.ml
@@ -16,6 +16,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
+open! Stdlib
 
 type t =
   { src : string option
diff --git a/compiler/lib/parse_js.ml b/compiler/lib/parse_js.ml
index 7981cf30b9..38d7a07b29 100644
--- a/compiler/lib/parse_js.ml
+++ b/compiler/lib/parse_js.ml
@@ -16,7 +16,9 @@
  * license.txt for more details.
  *)
 
-let strip_comment l = List.filter (fun x -> not (Js_token.is_comment x)) l
+open! Stdlib
+
+let strip_comment l = List.filter ~f:(fun x -> not (Js_token.is_comment x)) l
 
 let rec until_non_comment acc = function
   | [] -> acc, None
@@ -92,7 +94,7 @@ let lexer_aux ?(rm_comment = true) lines_info lexbuf =
     | _ ->
         let extra =
           match t with
-          | Js_token.TComment (ii, cmt) when String.length cmt > 1 && cmt.[0] = '#' -> (
+          | Js_token.TComment (ii, cmt) when String.is_prefix cmt ~prefix:"#" -> (
               let lexbuf = Lexing.from_string cmt in
               try
                 let file, line = Js_lexer.pos lexbuf in
@@ -128,11 +130,11 @@ let lexer_from_string ?rm_comment ?offset str : lexer =
   let lexbuf = Lexing.from_string str in
   lexer_aux ?rm_comment lines_info lexbuf
 
-let lexer_map = List.map
+let lexer_map f = List.map ~f
 
-let lexer_fold f acc l = List.fold_left f acc l
+let lexer_fold f acc l = List.fold_left ~f ~init:acc l
 
-let lexer_filter f l = List.filter f l
+let lexer_filter f l = List.filter ~f l
 
 let lexer_from_list l = adjust_tokens l
 
diff --git a/compiler/lib/phisimpl.ml b/compiler/lib/phisimpl.ml
index 6434076ec7..25fb24daa4 100644
--- a/compiler/lib/phisimpl.ml
+++ b/compiler/lib/phisimpl.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 
 let times = Debug.find "times"
 
@@ -125,7 +125,7 @@ module G = Dgraph.Make_Imperative (Var) (Var.ISet) (Var.Tbl)
 module Domain1 = struct
   type t = bool
 
-  let equal x y = x = y
+  let equal = Bool.equal
 
   let bot = false
 end
diff --git a/compiler/lib/pretty_print.ml b/compiler/lib/pretty_print.ml
index 519e18b728..56754c0411 100644
--- a/compiler/lib/pretty_print.ml
+++ b/compiler/lib/pretty_print.ml
@@ -18,6 +18,8 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
+open! Stdlib
+
 type pos =
   { mutable p_line : int
   ; mutable p_col : int }
@@ -54,7 +56,7 @@ let output st (s : string) l =
      let last = String.rindex_from s (l - 1) '\n' + 1 in
      let line = ref 0 in
      for i = 0 to l - 1 do
-       if s.[i] = '\n' then incr line
+       if Char.equal s.[i] '\n' then incr line
      done;
      st.line <- st.line + !line;
      st.col <- l - last
@@ -120,7 +122,7 @@ let rec push st e =
           let l = List.rev st.l in
           st.l <- [];
           st.n <- 0;
-          List.iter (fun e -> push st e) l)
+          List.iter ~f:(fun e -> push st e) l)
     | Set_pos _ -> ()
     | Start_group _ -> st.n <- st.n + 1
     | End_group ->
diff --git a/compiler/lib/primitive.ml b/compiler/lib/primitive.ml
index 56b3600e94..89c84c2853 100644
--- a/compiler/lib/primitive.ml
+++ b/compiler/lib/primitive.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 
 let aliases = Hashtbl.create 17
 
@@ -57,7 +57,7 @@ let arity nm = Hashtbl.find arities (resolve nm)
 
 let has_arity nm a = try Hashtbl.find arities (resolve nm) = a with Not_found -> false
 
-let is_pure nm = kind nm <> `Mutator
+let is_pure nm = Poly.(kind nm <> `Mutator)
 
 let exists p = Hashtbl.mem kinds p
 
diff --git a/compiler/lib/pseudoFs.ml b/compiler/lib/pseudoFs.ml
index b423b00793..1bf41888f3 100644
--- a/compiler/lib/pseudoFs.ml
+++ b/compiler/lib/pseudoFs.ml
@@ -17,7 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 
 let expand_path exts real virt =
   let rec loop realfile virtfile acc =
@@ -35,7 +35,7 @@ let expand_path exts real virt =
             List.mem e ~set:exts
           with Not_found -> List.mem "" ~set:exts
         in
-        if exts = [] || exmatch then (virtfile, realfile) :: acc else acc
+        if List.is_empty exts || exmatch then (virtfile, realfile) :: acc else acc
       with exc ->
         warn "ignoring %s: %s@." realfile (Printexc.to_string exc);
         acc
@@ -46,11 +46,11 @@ let list_files name paths =
   let name, virtname =
     match String.lsplit2 name ~on:':' with
     | Some (src, dest) ->
-        if String.length dest > 0 && dest.[0] <> '/'
+        if String.length dest > 0 && not (Char.equal dest.[0] '/')
         then
           failwith (Printf.sprintf "path '%s' for file '%s' must be absolute" dest src);
         let virtname =
-          if dest.[String.length dest - 1] = '/'
+          if Char.equal dest.[String.length dest - 1] '/'
           then dest ^ Filename.basename src
           else dest
         in
@@ -106,7 +106,7 @@ let f ~prim ~cmis ~files ~paths =
       cmis
       ([], [])
   in
-  if missing_cmis <> []
+  if not (List.is_empty missing_cmis)
   then (
     warn "Some OCaml interface files were not found.@.";
     warn "Use [-I dir_of_cmis] option to bring them into scope@.";
diff --git a/compiler/lib/pure_fun.ml b/compiler/lib/pure_fun.ml
index 84dfbbfb45..4beda6ffac 100644
--- a/compiler/lib/pure_fun.ml
+++ b/compiler/lib/pure_fun.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 open Code
 
 (****)
diff --git a/compiler/lib/reserved.ml b/compiler/lib/reserved.ml
index 89a81ecd07..de8b48bf22 100644
--- a/compiler/lib/reserved.ml
+++ b/compiler/lib/reserved.ml
@@ -17,7 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 
 let keyword =
   List.fold_left
diff --git a/compiler/lib/source_map.ml b/compiler/lib/source_map.ml
index 4fb1167d30..726b266b25 100644
--- a/compiler/lib/source_map.ml
+++ b/compiler/lib/source_map.ml
@@ -15,7 +15,9 @@
  * You should have received a copy of the GNU Lesser General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
- *)
+*)
+
+open! Stdlib
 
 type map =
   { gen_line : int
@@ -40,7 +42,7 @@ let string_of_mapping mapping =
   let a = Array.of_list mapping in
   let len = Array.length a in
   Array.stable_sort
-    (fun t1 t2 ->
+    ~cmp:(fun t1 t2 ->
       match compare t1.gen_line t2.gen_line with
       | 0 -> compare t1.gen_col t2.gen_col
       | n -> n)
@@ -173,7 +175,7 @@ let () =
   let map = mapping_of_string map_str in
   let map_str' = string_of_mapping map in
   (* let map' = mapping_of_string map_str' in *)
-  assert (map_str = map_str')
+  assert (String.equal map_str map_str')
 
 let merge_sources_content a b =
   match a, b with
@@ -206,7 +208,7 @@ let merge = function
               ; mappings =
                   acc.mappings
                   @ List.map
-                      (maps ~gen_line_offset ~sources_offset ~names_offset)
+                      ~f:(maps ~gen_line_offset ~sources_offset ~names_offset)
                       sm.mappings }
             in
             loop
@@ -218,8 +220,9 @@ let merge = function
       let acc =
         { x with
           mappings =
-            List.map (maps ~gen_line_offset ~sources_offset:0 ~names_offset:0) x.mappings
-        }
+            List.map
+              ~f:(maps ~gen_line_offset ~sources_offset:0 ~names_offset:0)
+              x.mappings }
       in
       Some
         (loop
diff --git a/compiler/lib/specialize.ml b/compiler/lib/specialize.ml
index 8242ae453e..efb00b060d 100644
--- a/compiler/lib/specialize.ml
+++ b/compiler/lib/specialize.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 open Code
 open Flow
 
diff --git a/compiler/lib/specialize_js.ml b/compiler/lib/specialize_js.ml
index 19804a991e..ef4059aef5 100644
--- a/compiler/lib/specialize_js.ml
+++ b/compiler/lib/specialize_js.ml
@@ -18,7 +18,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 open Code
 open Flow
 
@@ -134,20 +134,20 @@ let specialize_instr info i rem =
       :: rem
   | Let (x, Prim (Extern "%int_mul", [y; z])) ->
       (match the_int info y, the_int info z with
-      | Some j, _ when Int32.abs j < 0x200000l ->
+      | Some j, _ when Int32.(abs j < 0x200000l) ->
           Let (x, Prim (Extern "%direct_int_mul", [y; z]))
-      | _, Some j when Int32.abs j < 0x200000l ->
+      | _, Some j when Int32.(abs j < 0x200000l) ->
           Let (x, Prim (Extern "%direct_int_mul", [y; z]))
       | _ -> i)
       :: rem
   | Let (x, Prim (Extern "%int_div", [y; z])) ->
       (match the_int info z with
-      | Some j when j <> 0l -> Let (x, Prim (Extern "%direct_int_div", [y; z]))
+      | Some j when Int32.(j <> 0l) -> Let (x, Prim (Extern "%direct_int_div", [y; z]))
       | _ -> i)
       :: rem
   | Let (x, Prim (Extern "%int_mod", [y; z])) ->
       (match the_int info z with
-      | Some j when j <> 0l -> Let (x, Prim (Extern "%direct_int_mod", [y; z]))
+      | Some j when Int32.(j <> 0l) -> Let (x, Prim (Extern "%direct_int_mod", [y; z]))
       | _ -> i)
       :: rem
   | _ -> i :: rem
diff --git a/compiler/lib/stdlib.ml b/compiler/lib/stdlib.ml
index 35eceb664d..d7031b11d2 100644
--- a/compiler/lib/stdlib.ml
+++ b/compiler/lib/stdlib.ml
@@ -14,7 +14,49 @@
  * You should have received a copy of the GNU Lesser General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
- *)
+*)
+
+module Poly = struct
+  external ( < ) : 'a -> 'a -> bool = "%lessthan"
+
+  external ( <= ) : 'a -> 'a -> bool = "%lessequal"
+
+  external ( <> ) : 'a -> 'a -> bool = "%notequal"
+
+  external ( = ) : 'a -> 'a -> bool = "%equal"
+
+  external ( > ) : 'a -> 'a -> bool = "%greaterthan"
+
+  external ( >= ) : 'a -> 'a -> bool = "%greaterequal"
+
+  external compare : 'a -> 'a -> int = "%compare"
+
+  external equal : 'a -> 'a -> bool = "%equal"
+end
+
+module Int_replace_polymorphic_compare = struct
+  let ( < ) (x : int) y = x < y
+
+  let ( <= ) (x : int) y = x <= y
+
+  let ( <> ) (x : int) y = x <> y
+
+  let ( = ) (x : int) y = x = y
+
+  let ( > ) (x : int) y = x > y
+
+  let ( >= ) (x : int) y = x >= y
+
+  let compare (x : int) y = compare x y
+
+  let equal (x : int) y = x = y
+
+  let max (x : int) y = if x >= y then x else y
+
+  let min (x : int) y = if x <= y then x else y
+end
+
+include Int_replace_polymorphic_compare
 
 let quiet = ref false
 
@@ -82,6 +124,30 @@ module List = struct
           | x :: rest -> prev :: loop x rest
         in
         loop x xs
+
+  let is_empty = function
+    | [] -> true
+    | _ -> false
+end
+
+module Int32 = struct
+  include Int32
+
+  external ( < ) : int32 -> int32 -> bool = "%lessthan"
+
+  external ( <= ) : int32 -> int32 -> bool = "%lessequal"
+
+  external ( <> ) : int32 -> int32 -> bool = "%notequal"
+
+  external ( = ) : int32 -> int32 -> bool = "%equal"
+
+  external ( > ) : int32 -> int32 -> bool = "%greaterthan"
+
+  external ( >= ) : int32 -> int32 -> bool = "%greaterequal"
+
+  external compare : int32 -> int32 -> int = "%compare"
+
+  external equal : int32 -> int32 -> bool = "%equal"
 end
 
 module Option = struct
@@ -106,22 +172,84 @@ module Option = struct
     | None, Some _ -> -1
     | Some _, None -> 1
     | Some a, Some b -> compare_elt a b
+
+  let equal equal_elt a b =
+    match a, b with
+    | None, None -> true
+    | Some a, Some b -> equal_elt a b
+    | Some _, None | None, Some _ -> false
+
+  let is_none = function
+    | None -> true
+    | Some _ -> false
+
+  let is_some = function
+    | None -> false
+    | Some _ -> true
 end
 
-module Poly = struct
-  let compare : 'a. 'a -> 'a -> int = compare
+module Float = struct
+  include Float
+
+  external ( < ) : t -> t -> bool = "%lessthan"
+
+  external ( <= ) : t -> t -> bool = "%lessequal"
+
+  external ( <> ) : t -> t -> bool = "%notequal"
+
+  external ( = ) : t -> t -> bool = "%equal"
+
+  external ( > ) : t -> t -> bool = "%greaterthan"
+
+  external ( >= ) : t -> t -> bool = "%greaterequal"
+end
+
+module Bool = struct
+  external ( <> ) : bool -> bool -> bool = "%notequal"
+
+  external ( = ) : bool -> bool -> bool = "%equal"
 
-  let equal : 'a. 'a -> 'a -> bool = ( = )
+  external ( > ) : bool -> bool -> bool = "%greaterthan"
+
+  external equal : bool -> bool -> bool = "%equal"
 end
 
 module Char = struct
   include Char
 
+  external ( < ) : char -> char -> bool = "%lessthan"
+
+  external ( <= ) : char -> char -> bool = "%lessequal"
+
+  external ( <> ) : char -> char -> bool = "%notequal"
+
+  external ( = ) : char -> char -> bool = "%equal"
+
+  external ( > ) : char -> char -> bool = "%greaterthan"
+
+  external ( >= ) : char -> char -> bool = "%greaterequal"
+
+  external compare : char -> char -> int = "%compare"
+
+  external equal : char -> char -> bool = "%equal"
+
+  let is_alpha = function
+    | 'a' .. 'z' | 'A' .. 'Z' -> true
+    | _ -> false
+
+  let is_num = function
+    | '0' .. '9' -> true
+    | _ -> false
+
   let lowercase_ascii c =
-    if c >= 'A' && c <= 'Z' then Char.unsafe_chr (Char.code c + 32) else c
+    match c with
+    | 'A' .. 'Z' as c -> Char.unsafe_chr (Char.code c + 32)
+    | _ -> c
 
   let uppercase_ascii c =
-    if c >= 'a' && c <= 'z' then Char.unsafe_chr (Char.code c - 32) else c
+    match c with
+    | 'a' .. 'z' as c -> Char.unsafe_chr (Char.code c - 32)
+    | _ -> c
 end
 
 module Bytes = struct
@@ -131,12 +259,12 @@ module Bytes = struct
 end
 
 module String = struct
-  let equal (a : string) (b : string) = a = b
-
-  let _ = equal
-
   include StringLabels
 
+  let is_empty = function
+    | "" -> true
+    | _ -> false
+
   let is_prefix ~prefix s =
     let len_a = length prefix in
     let len_s = length s in
@@ -147,12 +275,24 @@ module String = struct
       let rec loop i =
         if i > max_idx_a
         then true
-        else if unsafe_get prefix i <> unsafe_get s i
+        else if not (Char.equal (unsafe_get prefix i) (unsafe_get s i))
         then false
         else loop (i + 1)
       in
       loop 0
 
+  let drop_prefix ~prefix s =
+    let plen = String.length prefix in
+    if plen > String.length s
+    then None
+    else
+      try
+        for i = 0 to String.length prefix - 1 do
+          if not (Char.equal s.[i] prefix.[i]) then raise Exit
+        done;
+        Some (String.sub s plen (String.length s - plen))
+      with Exit -> None
+
   let for_all =
     let rec loop s ~f ~last i =
       if i > last
@@ -166,14 +306,16 @@ module String = struct
   let is_ascii s =
     let res = ref true in
     for i = 0 to String.length s - 1 do
-      if s.[i] > '\127' then res := false
+      match s.[i] with
+      | '\000' .. '\127' -> ()
+      | '\128' .. '\255' -> res := false
     done;
     !res
 
   let has_backslash s =
     let res = ref false in
     for i = 0 to String.length s - 1 do
-      if s.[i] = '\\' then res := true
+      if Char.equal s.[i] '\\' then res := true
     done;
     !res
 
@@ -182,7 +324,7 @@ module String = struct
     let rec split beg cur =
       if cur >= len
       then if cur - beg > 0 then [String.sub p beg (cur - beg)] else []
-      else if p.[cur] = sep
+      else if Char.equal p.[cur] sep
       then String.sub p beg (cur - beg) :: split (cur + 1) (cur + 1)
       else split beg (cur + 1)
     in
@@ -217,14 +359,15 @@ module String = struct
              that no separator can be found we exit the loop and make a
              substring from [sub_start] until the end of the string. *)
           while !i + sep_max <= s_max do
-            if String.unsafe_get s !i <> String.unsafe_get sep 0
+            if not (Char.equal (String.unsafe_get s !i) (String.unsafe_get sep 0))
             then incr i
             else (
               (* Check remaining [sep] chars match, access to unsafe s (!i + !k) is
                    guaranteed by loop invariant. *)
               k := 1;
               while
-                !k <= sep_max && String.unsafe_get s (!i + !k) = String.unsafe_get sep !k
+                !k <= sep_max
+                && Char.equal (String.unsafe_get s (!i + !k)) (String.unsafe_get sep !k)
               do
                 incr k
               done;
diff --git a/compiler/lib/strongly_connected_components.ml b/compiler/lib/strongly_connected_components.ml
index 8fd22f2ca2..5f26c6cc7e 100644
--- a/compiler/lib/strongly_connected_components.ml
+++ b/compiler/lib/strongly_connected_components.ml
@@ -14,6 +14,8 @@
 (*                                                                        *)
 (**************************************************************************)
 
+open! Stdlib
+
 module IntSet = Set.Make (struct
   type t = int
 
@@ -31,7 +33,7 @@ end = struct
     let size = Array.length graph in
     let transposed = Array.make size [] in
     let add src dst = transposed.(src) <- dst :: transposed.(src) in
-    Array.iteri (fun src dsts -> List.iter (fun dst -> add dst src) dsts) graph;
+    Array.iteri ~f:(fun src dsts -> List.iter ~f:(fun dst -> add dst src) dsts) graph;
     transposed
 
   let depth_first_order (graph : int list array) : int array =
@@ -47,7 +49,7 @@ end = struct
       if not marked.(node)
       then (
         marked.(node) <- true;
-        List.iter aux graph.(node);
+        List.iter ~f:aux graph.(node);
         push node)
     in
     for i = 0 to size - 1 do
@@ -66,7 +68,7 @@ end = struct
       then (
         marked.(node) <- true;
         id.(node) <- !count;
-        List.iter aux graph.(node))
+        List.iter ~f:aux graph.(node))
     in
     for i = size - 1 downto 0 do
       let node = order.(i) in
@@ -92,16 +94,19 @@ end = struct
     let component_graph = Array.make ncomponents IntSet.empty in
     let add_component_dep node set =
       let node_deps = graph.(node) in
-      List.fold_left (fun set dep -> IntSet.add components.(dep) set) set node_deps
+      List.fold_left
+        ~f:(fun set dep -> IntSet.add components.(dep) set)
+        ~init:set
+        node_deps
     in
     Array.iteri
-      (fun node component ->
+      ~f:(fun node component ->
         id_scc.(component) <- node :: id_scc.(component);
         component_graph.(component) <- add_component_dep node component_graph.(component)
         )
       components;
     { sorted_connected_components = id_scc
-    ; component_edges = Array.map IntSet.elements component_graph }
+    ; component_edges = Array.map ~f:IntSet.elements component_graph }
 end
 
 module type S = sig
@@ -148,7 +153,7 @@ struct
     let size = Id.Map.cardinal graph in
     let bindings = Id.Map.bindings graph in
     let a = Array.of_list bindings in
-    let forth = Array.map fst a in
+    let forth = Array.map ~f:fst a in
     let back =
       let back = ref Id.Map.empty in
       for i = 0 to size - 1 do
@@ -157,7 +162,7 @@ struct
       !back
     in
     let integer_graph =
-      Array.init size (fun i ->
+      Array.init size ~f:(fun i ->
           let _, dests = a.(i) in
           Id.Set.fold
             (fun dest acc ->
@@ -174,19 +179,19 @@ struct
       Kosaraju.component_graph integer_graph
     in
     Array.mapi
-      (fun component nodes ->
+      ~f:(fun component nodes ->
         match nodes with
         | [] -> assert false
         | [node] ->
-            ( (if List.mem node integer_graph.(node)
+            ( (if List.mem node ~set:integer_graph.(node)
               then Has_loop [numbering.forth.(node)]
               else No_loop numbering.forth.(node))
             , component_edges.(component) )
         | _ :: _ ->
-            ( Has_loop (List.map (fun node -> numbering.forth.(node)) nodes)
+            ( Has_loop (List.map ~f:(fun node -> numbering.forth.(node)) nodes)
             , component_edges.(component) ))
       sorted_connected_components
 
   let connected_components_sorted_from_roots_to_leaf graph =
-    Array.map fst (component_graph graph)
+    Array.map ~f:fst (component_graph graph)
 end
diff --git a/compiler/lib/subst.ml b/compiler/lib/subst.ml
index f07b09e4bb..62a30869c0 100644
--- a/compiler/lib/subst.ml
+++ b/compiler/lib/subst.ml
@@ -18,7 +18,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 open Code
 
 let subst_cont s (pc, arg) = pc, List.map arg ~f:(fun x -> s x)
diff --git a/compiler/lib/tailcall.ml b/compiler/lib/tailcall.ml
index a7693d6466..0df4f9ee9b 100644
--- a/compiler/lib/tailcall.ml
+++ b/compiler/lib/tailcall.ml
@@ -17,7 +17,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
-open Stdlib
+open! Stdlib
 
 let times = Debug.find "times"
 
diff --git a/compiler/lib/timer.ml b/compiler/lib/timer.ml
index 0bf946b999..887c94ff62 100644
--- a/compiler/lib/timer.ml
+++ b/compiler/lib/timer.ml
@@ -14,7 +14,9 @@
  * You should have received a copy of the GNU Lesser General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
- *)
+*)
+
+open! Stdlib
 
 type t = float
 
diff --git a/compiler/lib/varPrinter.ml b/compiler/lib/varPrinter.ml
index 916aeb1044..5d5824d045 100644
--- a/compiler/lib/varPrinter.ml
+++ b/compiler/lib/varPrinter.ml
@@ -17,7 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Stdlib
+open! Stdlib
 
 module Alphabet = struct
   type t =
@@ -76,17 +76,13 @@ let propagate_name t v v' =
      *  with _ -> ()) *)
   with Not_found -> ()
 
-let is_alpha c = (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
-
-let is_num c = c >= '0' && c <= '9'
-
 let name t v nm_orig =
   let len = String.length nm_orig in
   if len > 0
   then (
     let buf = Buffer.create (String.length nm_orig) in
     let idx = ref 0 in
-    while !idx < len && not (is_alpha nm_orig.[!idx]) do
+    while !idx < len && not (Char.is_alpha nm_orig.[!idx]) do
       incr idx
     done;
     let pending = ref false in
@@ -95,7 +91,7 @@ let name t v nm_orig =
       pending := true;
       idx := 0);
     for i = !idx to len - 1 do
-      if is_alpha nm_orig.[i] || is_num nm_orig.[i]
+      if Char.is_alpha nm_orig.[i] || Char.is_num nm_orig.[i]
       then (
         if !pending then Buffer.add_char buf '_';
         Buffer.add_char buf nm_orig.[i];
diff --git a/compiler/lib/vlq64.ml b/compiler/lib/vlq64.ml
index c10a8680f6..83bb1e502e 100644
--- a/compiler/lib/vlq64.ml
+++ b/compiler/lib/vlq64.ml
@@ -15,7 +15,9 @@
  * You should have received a copy of the GNU Lesser General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
- *)
+*)
+
+open! Stdlib
 
 let code = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
 
@@ -69,7 +71,7 @@ let encode b x =
   let vql = toVLQSigned x in
   encode' b vql
 
-let encode_l b l = List.iter (encode b) l
+let encode_l b l = List.iter ~f:(encode b) l
 
 let rec decode' acc s start pos =
   let digit = code_rev.(Char.code s.[pos]) in
diff --git a/compiler/linkerArg.ml b/compiler/linkerArg.ml
index f85a9b49d8..75897db81b 100644
--- a/compiler/linkerArg.ml
+++ b/compiler/linkerArg.ml
@@ -17,6 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
+open! Js_of_ocaml_compiler.Stdlib
 open Js_of_ocaml_compiler
 open Cmdliner
 
diff --git a/compiler/minifyArg.ml b/compiler/minifyArg.ml
index 0120ba6714..f76b272f91 100644
--- a/compiler/minifyArg.ml
+++ b/compiler/minifyArg.ml
@@ -17,6 +17,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
+open! Js_of_ocaml_compiler.Stdlib
 open Js_of_ocaml_compiler
 open Cmdliner
 
diff --git a/compiler/util.ml b/compiler/util.ml
index 936b4c986b..55dff99856 100644
--- a/compiler/util.ml
+++ b/compiler/util.ml
@@ -16,7 +16,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *)
 
-open Js_of_ocaml_compiler.Stdlib
+open! Js_of_ocaml_compiler.Stdlib
 
 let normalize_argv ?(warn_ = false) a =
   let bad = ref [] in
@@ -26,7 +26,9 @@ let normalize_argv ?(warn_ = false) a =
         let size = String.length s in
         if size <= 2
         then s
-        else if s.[0] = '-' && s.[1] <> '-' && s.[2] <> '='
+        else if Char.equal s.[0] '-'
+                && (not (Char.equal s.[1] '-'))
+                && not (Char.equal s.[2] '=')
         then (
           bad := s :: !bad;
           (* long option with one dash lets double the dash *)
@@ -34,7 +36,7 @@ let normalize_argv ?(warn_ = false) a =
         else s)
       a
   in
-  if warn_ && !bad <> []
+  if warn_ && not (List.is_empty !bad)
   then
     warn
       "[Warning] long options with a single '-' are now deprecated. Please use '--' for \
diff --git a/toplevel/bin/jsoo_common.ml b/toplevel/bin/jsoo_common.ml
index ac31a553fa..79b8dbf3c9 100644
--- a/toplevel/bin/jsoo_common.ml
+++ b/toplevel/bin/jsoo_common.ml
@@ -29,7 +29,8 @@ let unit_of_cma filename =
   let ic = open_in_bin filename in
   let len_magic_number = String.length Config.cma_magic_number in
   let magic_number = input_s ic len_magic_number in
-  if magic_number <> Config.cma_magic_number then failwith "not a cma file";
+  if not (String.equal magic_number Config.cma_magic_number)
+  then failwith "not a cma file";
   let toc_pos = input_binary_int ic in
   seek_in ic toc_pos;
   let lib : Cmo_format.library = input_value ic in
@@ -73,7 +74,7 @@ let cmis_of_package pkg : string list =
     let add filename = fs := filename :: !fs in
     let archive =
       try Findlib.package_property ["byte"] pkg "archive"
-      with exc -> if pkg = "stdlib" then "stdlib.cma" else raise exc
+      with exc -> if String.equal pkg "stdlib" then "stdlib.cma" else raise exc
     in
     let l = String.split_char ~sep:' ' archive in
     List.iter l ~f:(fun x ->
diff --git a/toplevel/lib/jsooTop.ml b/toplevel/lib/jsooTop.ml
index dd3e8ac5a2..2e99b5fa5f 100644
--- a/toplevel/lib/jsooTop.ml
+++ b/toplevel/lib/jsooTop.ml
@@ -26,7 +26,7 @@ let split_primitives p =
   let rec split beg cur =
     if cur >= len
     then []
-    else if p.[cur] = '\000'
+    else if Char.equal p.[cur] '\000'
     then String.sub p ~pos:beg ~len:(cur - beg) :: split (cur + 1) (cur + 1)
     else split beg (cur + 1)
   in