diff --git a/AGENTS.md b/AGENTS.md
index a1a7f2ce9c8..9b5974bc0ff 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -72,6 +72,15 @@ JS IR
 JavaScript Code
 ```
 
+### Platform-specific compiler modules
+
+The Dune `browser` profile builds the playground compiler. Platform-dependent
+modules are stored below `platform/native/` and `platform/playground/` in their
+owning compiler directory. Rules in that directory's `dune` file copy the
+selected implementation into the build directory as an ordinary `.ml` module;
+all other profiles select the native source. Generated module paths in errors
+or stack traces therefore map back to one of those two source directories.
+
 ### Key Directory Structure
 
 ```
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 76551587577..eee2c3a2e70 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -35,6 +35,7 @@
 
 - Add the `-check-lam` compiler option, enable Lambda invariant checking in compiler tests, and remove build-profile-dependent checking. https://github.com/rescript-lang/rescript/pull/8534
 - Replace `-bs-diagnose` with `-debug-ir` and make IR diagnostic artifacts deterministic, compilation-local, and easy to clean. https://github.com/rescript-lang/rescript/pull/8535
+- Replace CPPO-based browser conditionals with Dune-selected native and playground compiler implementations. https://github.com/rescript-lang/rescript/pull/8541
 
 # 13.0.0-alpha.5
 
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 2802119dedb..46078febc0b 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -297,6 +297,20 @@ The "Playground bundle" is a JS version of the ReScript compiler; including all
 
 The ReScript source code is compiled with a tool called [JSOO (js_of_ocaml)](https://ocsigen.org/js_of_ocaml/latest/manual/overview), which uses OCaml bytecode to compile to JavaScript and is part of the bigger OCaml ecosystem.
 
+### Platform-specific compiler modules
+
+Within `compiler/`, the Dune `browser` profile specifically means the
+playground compiler. A few modules have implementations under
+`platform/native/` and `platform/playground/`; mutually exclusive rules in the
+owning `dune` file copy the appropriate implementation into the build directory
+as an ordinary `.ml` module. Other profiles select the native implementation.
+
+Consequently, a generated filename such as `ext_platform_primitives.ml` may
+appear in a compiler stack trace even though it is not present in the source
+tree. Its source is the corresponding file below `platform/native/` or
+`platform/playground/` in the same compiler directory. Keep both
+implementations API-compatible when changing one of these modules.
+
 ### Building the Bundle
 
 The entry point of the JSOO bundle is located in `compiler/jsoo/jsoo_playground_main.ml`, the compiler and its relevant runtime cmij files can be built via make:
@@ -310,9 +324,9 @@ Note that building the cmijs is based on the dependencies defined in `packages/p
 
 After a successful compilation, you will find following files in your project:
 
-- `playground/compiler.js` -> This is the ReScript compiler, which binds the ReScript API to the `window` object.
-- `playground/packages/compiler-builtins` -> The compiler base cmij containing all the relevant core modules (`Js`, `Belt`, `Pervasives`, etc.)
-- `playground/packages/*` -> Contains third party deps with cmij.js files (as defined in `packages/playground/rescript.json`)
+- `packages/playground/compiler.js` -> This is the ReScript compiler, which binds the ReScript API to the `window` object.
+- `packages/playground/packages/compiler-builtins` -> The compiler base cmij containing all the relevant core modules (`Js`, `Belt`, `Pervasives`, etc.)
+- `packages/playground/packages/*` -> Contains third party deps with cmij.js files (as defined in `packages/playground/rescript.json`)
 
 You can now use the `compiler.js` file either directly by using a `<script src="/path/to/compiler.js"/>` and `<script src="/path/to/packages/compilerCmij.js"/>` inside a html file, use a browser bundler infrastructure to optimize it, or use `nodejs` to run it on a command line:
 
diff --git a/compiler/core/build_artifact_stubs.c b/compiler/core/build_artifact_stubs.c
new file mode 100644
index 00000000000..2a578fd06ca
--- /dev/null
+++ b/compiler/core/build_artifact_stubs.c
@@ -0,0 +1,33 @@
+#include "caml/memory.h"
+#include "caml/mlvalues.h"
+#include "caml/osdeps.h"
+#include "caml/signals.h"
+
+#ifdef _WIN32
+#include <sys/utime.h>
+
+CAMLprim value caml_stale_file(value path)
+{
+  CAMLparam1(path);
+  struct _utimbuf times;
+  char *os_path = caml_stat_strdup(String_val(path));
+  times.modtime = 0;
+  caml_enter_blocking_section();
+  _utime(os_path, &times);
+  caml_leave_blocking_section();
+  caml_stat_free(os_path);
+  CAMLreturn(Val_unit);
+}
+#else
+#include <sys/time.h>
+
+CAMLprim value caml_stale_file(value path)
+{
+  CAMLparam1(path);
+  struct timeval times[2] = {{0, 0}, {0, 0}};
+  char *os_path = caml_stat_strdup_to_os(String_val(path));
+  utimes(os_path, times);
+  caml_stat_free(os_path);
+  CAMLreturn(Val_unit);
+}
+#endif
diff --git a/compiler/core/dune b/compiler/core/dune
index 261b0deda02..7029e11d807 100644
--- a/compiler/core/dune
+++ b/compiler/core/dune
@@ -1,20 +1,44 @@
-(library
- (name core)
- (wrapped false)
- (instrumentation
-  (backend bisect_ppx))
- (flags
-  (:standard -w +a-4-9-27-30-40-41-42-48-70))
- (libraries depends ext flow_parser frontend gentype yojson))
+(env
+ (_
+  (flags
+   (:standard -w +a-4-9-27-30-40-41-42-48-70))))
+
+; The browser profile builds the playground compiler; these rules generate modules from platform/{native,playground}.
+
+(rule
+ (target build_artifact.ml)
+ (enabled_if
+  (= %{profile} browser))
+ (action
+  (copy platform/playground/build_artifact.ml build_artifact.ml)))
+
+(rule
+ (target build_artifact.ml)
+ (enabled_if
+  (<> %{profile} browser))
+ (action
+  (copy platform/native/build_artifact.ml build_artifact.ml)))
 
 (rule
  (target js_name_of_module_id.ml)
- (deps js_name_of_module_id.cppo.ml)
+ (enabled_if
+  (= %{profile} browser))
  (action
-  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+  (copy platform/playground/js_name_of_module_id.ml js_name_of_module_id.ml)))
 
 (rule
- (target lam_compile_main.ml)
- (deps lam_compile_main.cppo.ml)
+ (target js_name_of_module_id.ml)
+ (enabled_if
+  (<> %{profile} browser))
  (action
-  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+  (copy platform/native/js_name_of_module_id.ml js_name_of_module_id.ml)))
+
+(library
+ (name core)
+ (wrapped false)
+ (instrumentation
+  (backend bisect_ppx))
+ (foreign_stubs
+  (language c)
+  (names build_artifact_stubs))
+ (libraries depends ext flow_parser frontend gentype yojson))
diff --git a/compiler/core/js_name_of_module_id.cppo.ml b/compiler/core/js_name_of_module_id.cppo.ml
deleted file mode 100644
index a954db439c6..00000000000
--- a/compiler/core/js_name_of_module_id.cppo.ml
+++ /dev/null
@@ -1,167 +0,0 @@
-(* Copyright (C) 2017 Hongbo Zhang, Authors of ReScript
- * 
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU Lesser General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * In addition to the permissions granted to you by the LGPL, you may combine
- * or link a "work that uses the Library" with a publicly distributed version
- * of this file to produce a combined library or application, then distribute
- * that combined work under the terms of your choosing, with no requirement
- * to comply with the obligations normally placed on you by section 4 of the
- * LGPL version 3 (or the corresponding section of a later version of the LGPL
- * should you choose to use a later version).
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU Lesser General Public License for more details.
- * 
- * 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. *)
-(*
-let (=)  (x : int) (y:float) = assert false 
-*)
-
-#ifdef BROWSER
-
-let string_of_module_id_in_browser (x : Lam_module_ident.t) =  
-  match x.kind with
-  | External {name} -> name
-  | Runtime | Ml -> 
-    "./stdlib/" ^ x.id.name ^ ".mjs"
-
-let string_of_module_id 
-    (id : Lam_module_ident.t)
-    ~output_dir:(_:string)
-    (_module_system : Js_packages_info.module_system)
-  = string_of_module_id_in_browser id
-
-#else
-  
-let (//) = Filename.concat 
-
-
-let fix_path_for_windows : string -> string = 
-  if Ext_sys.is_windows_or_cygwin then Ext_string.replace_backward_slash
-  else fun s -> s 
-
-let runtime_suffix_of_module_system (module_system : Js_packages_info.module_system)
-    =
-  match module_system with
-  | Commonjs -> ".cjs"
-  | Esmodule -> ".mjs"
-
-(* dependency is runtime module *)  
-let get_runtime_module_path 
-    (dep_module_id : Lam_module_ident.t) 
-    (current_package_info : Js_packages_info.t)
-    (module_system : Js_packages_info.module_system) = 
-  let current_info_query = 
-    Js_packages_info.query_package_infos current_package_info
-      module_system  in
-  let js_file =  
-    Ext_namespace.js_name_of_modulename dep_module_id.id.name 
-      Upper (runtime_suffix_of_module_system module_system) in 
-  match current_info_query with        
-  | Package_not_found -> assert false
-  | Package_script -> 
-    Js_packages_info.runtime_package_path module_system js_file          
-  | Package_found pkg -> 
-    let  dep_path  = 
-      "lib" // Js_packages_info.runtime_dir_of_module_system module_system in 
-    if  Js_packages_info.is_runtime_package current_package_info then 
-      Ext_path.node_rebase_file
-        ~from:pkg.rel_path
-        ~to_:dep_path 
-        js_file
-        (* TODO: we assume that both [x] and [path] could only be relative path
-            which is guaranteed by [-bs-package-output]
-        *)
-    else  
-      Js_packages_info.runtime_package_path module_system js_file              
-
-(* [output_dir] is decided by the command line argument *)
-let string_of_module_id 
-    (dep_module_id : Lam_module_ident.t) 
-    ~(output_dir : string )
-    (module_system : Js_packages_info.module_system)        
-  : string =
-  let current_package_info = Js_packages_state.get_packages_info ()  in 
-  fix_path_for_windows (    
-    match dep_module_id.kind  with 
-    | External {name} -> name (* the literal string for external package *)
-    (* This may not be enough, 
-        1. For cross packages, we may need settle 
-        down a single js package
-        2. We may need es6 path for dead code elimination
-         But frankly, very few JS packages have no dependency, 
-         so having plugin may sound not that bad   
-    *)
-    | Runtime  -> 
-      get_runtime_module_path dep_module_id current_package_info module_system
-    | Ml  -> 
-      let current_info_query = 
-        Js_packages_info.query_package_infos 
-          current_package_info
-          module_system  
-      in
-      match Lam_compile_env.get_package_path_from_cmj dep_module_id with 
-      | (package_path, dep_package_info, case) -> 
-
-
-        let dep_info_query =  
-          Js_packages_info.query_package_infos dep_package_info module_system 
-        in 
-        match dep_info_query, current_info_query with
-        | Package_not_found , _  -> 
-          Bs_exception.error (Missing_ml_dependency dep_module_id.id.name)
-        | Package_script , Package_found _  -> 
-          Bs_exception.error (Dependency_script_module_dependent_not dep_module_id.id.name)
-        | (Package_script  | Package_found _ ), Package_not_found -> assert false
-
-        | Package_found ({suffix} as pkg), Package_script 
-          ->    
-          let js_file =  
-            Ext_namespace.js_name_of_modulename dep_module_id.id.name case suffix in 
-          pkg.pkg_rel_path // js_file
-        | Package_found ({suffix } as dep_pkg),
-          Package_found cur_pkg -> 
-          let js_file =  
-            Ext_namespace.js_name_of_modulename dep_module_id.id.name case suffix in 
-
-          if  Js_packages_info.same_package_by_name current_package_info  dep_package_info then 
-            Ext_path.node_rebase_file
-              ~from:cur_pkg.rel_path
-              ~to_:dep_pkg.rel_path 
-              js_file
-              (* TODO: we assume that both [x] and [path] could only be relative path
-                  which is guaranteed by [-bs-package-output]
-              *)
-          else  
-          if Js_packages_info.is_runtime_package dep_package_info then 
-            get_runtime_module_path dep_module_id current_package_info module_system
-          else dep_pkg.pkg_rel_path // js_file
-        | Package_script, Package_script 
-          -> 
-          let js_file =  
-            Ext_namespace.js_name_of_modulename dep_module_id.id.name case Literals.suffix_js in 
-          match Config_util.find_opt js_file with 
-          | Some file -> 
-            let basename = Filename.basename file in 
-            let dirname = Filename.dirname file in 
-            Ext_path.node_rebase_file
-              ~from:(
-                Ext_path.absolute_cwd_path 
-                  output_dir)
-              ~to_:(
-                Ext_path.absolute_cwd_path 
-
-                  dirname)
-              basename  
-          | None -> 
-            Bs_exception.error (Js_not_found js_file))
-
-#endif
diff --git a/compiler/core/lam_compile_main.cppo.ml b/compiler/core/lam_compile_main.cppo.ml
deleted file mode 100644
index 884c06afb02..00000000000
--- a/compiler/core/lam_compile_main.cppo.ml
+++ /dev/null
@@ -1,399 +0,0 @@
-(* Copyright (C) 2015 - 2016 Bloomberg Finance L.P.
- * Copyright (C) 2017 - Hongbo Zhang, Authors of ReScript 
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU Lesser General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * In addition to the permissions granted to you by the LGPL, you may combine
- * or link a "work that uses the Library" with a publicly distributed version
- * of this file to produce a combined library or application, then distribute
- * that combined work under the terms of your choosing, with no requirement
- * to comply with the obligations normally placed on you by section 4 of the
- * LGPL version 3 (or the corresponding section of a later version of the LGPL
- * should you choose to use a later version).
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU Lesser General Public License for more details.
- * 
- * 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 E = Js_exp_make  *)
-(* module S = Js_stmt_make   *)
-
-
-let compile_group output_prefix (meta : Lam_stats.t) 
-    (x : Lam_group.t) : Js_output.t  = 
-  match x with 
-  (* 
-        We need
-
-        2. [E.builtin_dot] for javascript builtin
-        3. [E.mldot]
-     *)
-  (* ATTENTION: check {!Lam_compile_global} for consistency  *)      
-  (* Special handling for values in [Pervasives] *)  
-  (* 
-         we delegate [stdout, stderr, and stdin] into [caml_io] module, 
-         the motivation is to help dead code eliminatiion, it's helpful 
-         to make those parts pure (not a function call), then it can be removed 
-         if unused 
-      *)                     
-
-  (* QUICK hack to make hello world example nicer,
-     Note the arity of [print_endline] is already analyzed before, 
-     so it should be safe
-  *)
-
-  | Single (kind, id, lam) -> 
-    (* let lam = Optimizer.simplify_lets [] lam in  *)
-    (* can not apply again, it's wrong USE it with care*)
-    (* ([Js_stmt_make.comment (Gen_of_env.query_type id  env )], None)  ++ *)
-    Lam_compile.compile_lambda ~output_prefix { continuation = Declare (kind, id);
-                                 jmp_table = Lam_compile_context.empty_handler_map;
-                                 switch_depth = 0;
-                                 loop_stack = [];
-                                 loop_label_counter = ref 0;
-                                 meta
-                               } lam
-
-  | Recursive id_lams   -> 
-    Lam_compile.compile_recursive_lets ~output_prefix
-      { continuation = EffectCall Not_tail; 
-        jmp_table = Lam_compile_context.empty_handler_map;
-        switch_depth = 0;
-        loop_stack = [];
-        loop_label_counter = ref 0;
-        meta
-      } 
-      id_lams
-  | Nop lam -> (* TODO: Side effect callls, log and see statistics *)
-    Lam_compile.compile_lambda ~output_prefix {continuation = EffectCall Not_tail;
-                                jmp_table = Lam_compile_context.empty_handler_map;
-                                switch_depth = 0;
-                                loop_stack = [];
-                                loop_label_counter = ref 0;
-                                meta
-                               } lam
-
-;;
-
-(** Also need analyze its depenency is pure or not *)
-let no_side_effects (rest : Lam_group.t list) : string option = 
-  Ext_list.find_opt rest (fun x -> 
-      match x with 
-      | Single(kind,id,body) -> 
-        begin 
-          match kind with 
-          | Strict | Variable -> 
-            if not @@ Lam_analysis.no_side_effects body 
-            then Some  (Printf.sprintf "%s" id.name)
-            else None
-          | _ -> None
-        end
-      | Recursive bindings -> 
-        Ext_list.find_opt  bindings (fun (id,lam) -> 
-            if not @@ Lam_analysis.no_side_effects lam 
-            then Some (Printf.sprintf "%s" id.Ident.name )
-            else None
-          )
-      | Nop lam -> 
-        if not @@ Lam_analysis.no_side_effects lam 
-        then 
-          (*  (Lam_util.string_of_lambda lam) *)
-          Some ""
-        else None (* TODO :*))
-
-
-(** Actually simplify_lets is kind of global optimization since it requires you to know whether 
-    it's used or not 
-*)
-let compile  
-    (output_prefix : string)
-    export_idents
-    (lam : Lambda.lambda)  = 
-  let debug_ir = !Js_config.debug_ir in
-  let diagnostics =
-    if debug_ir then Some (Ir_diagnostics.create ~output_prefix) else None
-  in
-  let d pass lam =
-    (match diagnostics with
-    | Some diagnostics ->
-      Ir_diagnostics.dump_lam diagnostics ~pass lam;
-      Ext_log.dwarn ~__POS__ "START CHECKING PASS %s@." pass
-    | None -> ());
-    if !Js_config.check_lam || debug_ir then begin
-      ignore @@ Lam_check.check ~file:!Location.input_name ~pass lam;
-      if debug_ir then Ext_log.dwarn ~__POS__ "FINISH CHECKING PASS %s@." pass
-    end;
-    lam
-  in
-  let j pass program =
-    Ext_option.iter diagnostics (fun diagnostics ->
-        Ir_diagnostics.dump_js diagnostics ~pass program);
-    program
-  in
-  let export_ident_sets = Set_ident.of_list export_idents in 
-  (* To make toplevel happy - reentrant for js-demo *)
-  let () =
-    if debug_ir then begin
-      Ext_list.iter export_idents 
-        (fun id -> Ext_log.dwarn ~__POS__ "export idents: %s/%d" id.name id.stamp)
-    end;
-    Lam_compile_env.reset ()
-  in
-  let lam, may_required_modules = Lam_convert.convert export_ident_sets lam in 
-
-
-  let lam = d "initial"  lam in
-  let lam  = Lam_pass_deep_flatten.deep_flatten lam in
-  let lam = d  "flatten0" lam in
-  let meta  : Lam_stats.t = 
-    Lam_stats.make 
-      ~export_idents
-      ~export_ident_sets in 
-  let () = Lam_pass_collect.collect_info meta lam in 
-  let lam = 
-    let lam =  
-      lam
-      |> d "flatten1"
-      |>  Lam_pass_exits.simplify_exits
-      |> d "simplify_exits"
-      |> (fun lam ->
-          Lam_pass_collect.collect_info meta lam;
-          if debug_ir then
-            Ext_log.dwarn ~__POS__ "Before simplify_alias: %a@." Lam_stats.print
-              meta;
-          lam)
-      |>  Lam_pass_remove_alias.simplify_alias  meta
-      |> d "simplify_alias"
-      |> Lam_pass_deep_flatten.deep_flatten
-      |> d  "flatten2"
-    in  (* Inling happens*)
-
-    let ()  = Lam_pass_collect.collect_info meta lam in
-    let lam = Lam_pass_remove_alias.simplify_alias meta lam  in
-    let lam = Lam_pass_deep_flatten.deep_flatten lam in
-    let ()  = Lam_pass_collect.collect_info meta lam in
-    let lam = 
-      lam
-      |> d "alpha_before"
-      |> Lam_pass_alpha_conversion.alpha_conversion meta
-      |> d "alpha_after"
-      |> Lam_pass_exits.simplify_exits in    
-    let () = Lam_pass_collect.collect_info meta lam in
-
-
-    lam
-    |> d "simplify_alias_before"
-    |>  Lam_pass_remove_alias.simplify_alias meta 
-    |> d "alpha_conversion"
-    |>  Lam_pass_alpha_conversion.alpha_conversion meta
-    |> d  "before-simplify_lets"
-    (* we should investigate a better way to put different passes : )*)
-    |> Lam_pass_lets_dce.simplify_lets 
-
-    |> d "before-simplify-exits"
-    (* |> (fun lam -> Lam_pass_collect.collect_info meta lam 
-       ; Lam_pass_remove_alias.simplify_alias meta lam) *)
-    (* |> Lam_group_pass.scc_pass
-       |> d "scc" *)
-    |> Lam_pass_exits.simplify_exits
-    |> d "simplify_lets"
-    |> (fun lam ->
-        if debug_ir then
-          Ext_log.dwarn ~__POS__ "Before coercion: %a@." Lam_stats.print meta;
-        lam)
-  in
-
-  let ({Lam_coercion.groups = groups } as coerced_input , meta) = 
-    Lam_coercion.coerce_and_group_big_lambda  meta lam
-  in 
-
-let () =
-  if debug_ir then begin
-    Ext_log.dwarn ~__POS__ "After coercion: %a@." Lam_stats.print meta;
-    Ext_option.iter diagnostics (fun diagnostics ->
-        Ir_diagnostics.dump_groups diagnostics coerced_input.groups)
-  end
-in
-let maybe_pure = no_side_effects groups in
-let () =
-  if debug_ir then
-    Ext_log.dwarn ~__POS__ "\n@[[TIME:]Pre-compile: %f@]@."
-      (Sys.time () *. 1000.)
-in
-let body  =     
-  Ext_list.map groups (fun group -> compile_group output_prefix meta group)
-  |> Js_output.concat
-  |> Js_output.output_as_block
-in
-let () =
-  if debug_ir then
-    Ext_log.dwarn ~__POS__ "\n@[[TIME:]Post-compile: %f@]@."
-      (Sys.time () *. 1000.)
-in
-(* The file is not big at all compared with [cmo] *)
-(* Ext_marshal.to_file (Ext_path.chop_extension filename ^ ".mj")  js; *)
-let meta_exports = meta.exports in 
-let export_set = Set_ident.of_list meta_exports in 
-let js : J.program = 
-  { 
-    exports = meta_exports ; 
-    export_set; 
-    block = body}
-in
-js 
-|> j "initial"
-|> Js_pass_flatten.program
-|> j "flatten"
-|> Js_pass_external_shadow.program
-|> j "external_shadow"
-|> Js_pass_tailcall_inline.tailcall_inline
-|> j "inline_and_shake"
-|> Js_pass_record_rest.program
-|> j "record_rest"
-|> Js_pass_flatten_and_mark_dead.program
-|> j "flatten_and_mark_dead"
-(* |> Js_inline_and_eliminate.inline_and_shake *)
-(* |> j "inline_and_shake" *)
-|> (fun js -> ignore @@ Js_pass_scope.program  js ; js )
-|> Js_shake.shake_program
-|> j "shake"
-|> ( fun (program:  J.program) -> 
-    let external_module_ids : Lam_module_ident.t list = 
-      if !Js_config.all_module_aliases then []
-      else
-        let hard_deps = 
-          Js_fold_basic.calculate_hard_dependencies program.block in  
-        Lam_compile_env.populate_required_modules  
-          may_required_modules hard_deps ;        
-        Ext_list.sort_via_array (Lam_module_ident.Hash_set.to_list hard_deps)
-          (fun id1 id2 ->
-             Ext_string.compare (Lam_module_ident.name id1) (Lam_module_ident.name id2)
-          ) 
-    in
-    Warnings.check_fatal();
-    let effect_ = 
-      Lam_stats_export.get_dependent_module_effect
-        maybe_pure external_module_ids in 
-    let v : Js_cmj_format.t = 
-      Lam_stats_export.export_to_cmj 
-        meta  
-        effect_ 
-        coerced_input.export_map          
-        (if Ext_char.is_lower_case (Filename.basename output_prefix).[0] then Little else Upper)
-    in
-    (if not !Clflags.dont_write_files then
-       Js_cmj_format.to_file 
-         ~check_exists:(not !Js_config.force_cmj)
-         (output_prefix ^ Literals.suffix_cmj) v);
-    {J.program = program ; side_effect = effect_ ; modules = external_module_ids }      
-  )
-;;
-
-let (//) = Filename.concat  
-
-let remove_stale_source_map ?(remove_stale_map = true) target_file =
-  if remove_stale_map && not !Clflags.dont_write_files then
-    Misc.remove_file (target_file ^ ".map")
-
-let dump_deps_program_with_source_map ?(remove_stale_map = true) ~target_file
-    ~output_prefix module_system lambda_output chan =
-  let builder =
-    Js_source_map.make ~generated_file:target_file
-      ~source_root:!Js_config.source_map_root
-      ~sources_content:!Js_config.source_map_sources_content
-  in
-  Js_source_map.with_builder builder (fun () ->
-      Js_dump_program.pp_deps_program ~output_prefix module_system lambda_output
-        (Ext_pp.from_channel chan));
-  match !Js_config.source_map with
-  | Linked ->
-    let json = Js_source_map.json builder in
-    output_string chan (Js_source_map.linked_comment ~map_file:(target_file ^ ".map"));
-    Ext_io.write_file (target_file ^ ".map") json
-  | Hidden -> Ext_io.write_file (target_file ^ ".map") (Js_source_map.json builder)
-  | Inline ->
-    output_string chan
-      (Js_source_map.inline_comment ~json:(Js_source_map.json builder));
-    remove_stale_source_map ~remove_stale_map target_file
-  | No_source_map -> ()
-
-let lambda_as_module 
-    (lambda_output : J.deps_program)
-    (output_prefix : string)
-  : unit = 
-  let package_info = Js_packages_state.get_packages_info () in 
-  if Js_packages_info.is_empty package_info && !Js_config.js_stdout then begin    
-    match !Js_config.source_map with
-    | Inline ->
-      let target_file =
-        Ext_namespace.change_ext_ns_suffix
-          (Filename.basename output_prefix)
-          Literals.suffix_js
-      in
-      dump_deps_program_with_source_map ~remove_stale_map:false ~target_file
-        ~output_prefix Commonjs lambda_output stdout
-    | _ ->
-      Js_dump_program.dump_deps_program ~output_prefix Commonjs lambda_output
-        stdout
-  end else
-    Js_packages_info.iter package_info (fun {module_system; path; suffix} -> 
-        let basename =  
-          Ext_namespace.change_ext_ns_suffix (Filename.basename output_prefix) suffix
-        in
-        let target_file =
-          (Ext_path.package_dir () //
-           path //
-           basename
-           (* #913 only generate little-case js file *)
-          ) in
-        let output_chan chan =
-          match !Js_config.source_map with
-          | No_source_map ->
-            Js_dump_program.dump_deps_program ~output_prefix module_system
-              lambda_output chan;
-            remove_stale_source_map target_file
-          | Linked | Inline | Hidden ->
-            dump_deps_program_with_source_map ~target_file ~output_prefix
-              module_system lambda_output chan
-        in
-        (if not !Clflags.dont_write_files then 
-           Ext_pervasives.with_file_as_chan
-             target_file output_chan );
-        if !Warnings.has_warnings  then begin 
-          Warnings.has_warnings := false ;
-#ifndef BROWSER
-          (* 5206: When there were warnings found during the compilation, we want the file
-             to be rebuilt on the next "rescript build" so that the warnings keep being shown.
-             Set the timestamp of the ast file to 1970-01-01 to make this rebuild happen.
-             (Do *not* set the timestamp of the JS output file instead
-             as that does not play well with every bundler.) *)
-          let ast_file = output_prefix ^ Literals.suffix_ast in
-          if Sys.file_exists ast_file then begin 
-            Bs_hash_stubs.set_as_old_file ast_file
-          end          
-#endif          
-        end             
-      )
-
-
-
-(* We can use {!Env.current_unit = "Pervasives"} to tell if it is some specific module, 
-    We need handle some definitions in standard libraries in a special way, most are io specific, 
-    includes {!Pervasives.stdin, Pervasives.stdout, Pervasives.stderr}
-
-    However, use filename instead of {!Env.current_unit} is more honest, since node-js module system is coupled with the file name 
-*)
diff --git a/compiler/core/lam_compile_main.ml b/compiler/core/lam_compile_main.ml
new file mode 100644
index 00000000000..4db6c659179
--- /dev/null
+++ b/compiler/core/lam_compile_main.ml
@@ -0,0 +1,348 @@
+(* Copyright (C) 2015 - 2016 Bloomberg Finance L.P.
+ * Copyright (C) 2017 - Hongbo Zhang, Authors of ReScript
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * In addition to the permissions granted to you by the LGPL, you may combine
+ * or link a "work that uses the Library" with a publicly distributed version
+ * of this file to produce a combined library or application, then distribute
+ * that combined work under the terms of your choosing, with no requirement
+ * to comply with the obligations normally placed on you by section 4 of the
+ * LGPL version 3 (or the corresponding section of a later version of the LGPL
+ * should you choose to use a later version).
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * 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 E = Js_exp_make  *)
+(* module S = Js_stmt_make   *)
+
+let compile_group output_prefix (meta : Lam_stats.t) (x : Lam_group.t) :
+    Js_output.t =
+  match x with
+  (*
+        We need
+
+        2. [E.builtin_dot] for javascript builtin
+        3. [E.mldot]
+     *)
+  (* ATTENTION: check {!Lam_compile_global} for consistency  *)
+  (* Special handling for values in [Pervasives] *)
+  (*
+         we delegate [stdout, stderr, and stdin] into [caml_io] module,
+         the motivation is to help dead code eliminatiion, it's helpful
+         to make those parts pure (not a function call), then it can be removed
+         if unused
+      *)
+
+  (* QUICK hack to make hello world example nicer,
+     Note the arity of [print_endline] is already analyzed before,
+     so it should be safe
+  *)
+  | Single (kind, id, lam) ->
+    (* let lam = Optimizer.simplify_lets [] lam in  *)
+    (* can not apply again, it's wrong USE it with care*)
+    (* ([Js_stmt_make.comment (Gen_of_env.query_type id  env )], None)  ++ *)
+    Lam_compile.compile_lambda ~output_prefix
+      {
+        continuation = Declare (kind, id);
+        jmp_table = Lam_compile_context.empty_handler_map;
+        switch_depth = 0;
+        loop_stack = [];
+        loop_label_counter = ref 0;
+        meta;
+      }
+      lam
+  | Recursive id_lams ->
+    Lam_compile.compile_recursive_lets ~output_prefix
+      {
+        continuation = EffectCall Not_tail;
+        jmp_table = Lam_compile_context.empty_handler_map;
+        switch_depth = 0;
+        loop_stack = [];
+        loop_label_counter = ref 0;
+        meta;
+      }
+      id_lams
+  | Nop lam ->
+    (* TODO: Side effect callls, log and see statistics *)
+    Lam_compile.compile_lambda ~output_prefix
+      {
+        continuation = EffectCall Not_tail;
+        jmp_table = Lam_compile_context.empty_handler_map;
+        switch_depth = 0;
+        loop_stack = [];
+        loop_label_counter = ref 0;
+        meta;
+      }
+      lam
+
+(** Also need analyze its depenency is pure or not *)
+let no_side_effects (rest : Lam_group.t list) : string option =
+  Ext_list.find_opt rest (fun x ->
+      match x with
+      | Single (kind, id, body) -> (
+        match kind with
+        | Strict | Variable ->
+          if not @@ Lam_analysis.no_side_effects body then
+            Some (Printf.sprintf "%s" id.name)
+          else None
+        | _ -> None)
+      | Recursive bindings ->
+        Ext_list.find_opt bindings (fun (id, lam) ->
+            if not @@ Lam_analysis.no_side_effects lam then
+              Some (Printf.sprintf "%s" id.Ident.name)
+            else None)
+      | Nop lam ->
+        if not @@ Lam_analysis.no_side_effects lam then
+          (*  (Lam_util.string_of_lambda lam) *)
+          Some ""
+        else None (* TODO :*))
+
+(** Actually simplify_lets is kind of global optimization since it requires you to know whether
+    it's used or not
+*)
+let compile (output_prefix : string) export_idents (lam : Lambda.lambda) =
+  let debug_ir = !Js_config.debug_ir in
+  let diagnostics =
+    if debug_ir then Some (Ir_diagnostics.create ~output_prefix) else None
+  in
+  let d pass lam =
+    (match diagnostics with
+    | Some diagnostics ->
+      Ir_diagnostics.dump_lam diagnostics ~pass lam;
+      Ext_log.dwarn ~__POS__ "START CHECKING PASS %s@." pass
+    | None -> ());
+    if !Js_config.check_lam || debug_ir then (
+      ignore @@ Lam_check.check ~file:!Location.input_name ~pass lam;
+      if debug_ir then Ext_log.dwarn ~__POS__ "FINISH CHECKING PASS %s@." pass);
+    lam
+  in
+  let j pass program =
+    Ext_option.iter diagnostics (fun diagnostics ->
+        Ir_diagnostics.dump_js diagnostics ~pass program);
+    program
+  in
+  let export_ident_sets = Set_ident.of_list export_idents in
+  (* To make toplevel happy - reentrant for js-demo *)
+  let () =
+    if debug_ir then
+      Ext_list.iter export_idents (fun id ->
+          Ext_log.dwarn ~__POS__ "export idents: %s/%d" id.name id.stamp);
+    Lam_compile_env.reset ()
+  in
+  let lam, may_required_modules = Lam_convert.convert export_ident_sets lam in
+
+  let lam = d "initial" lam in
+  let lam = Lam_pass_deep_flatten.deep_flatten lam in
+  let lam = d "flatten0" lam in
+  let meta : Lam_stats.t = Lam_stats.make ~export_idents ~export_ident_sets in
+  let () = Lam_pass_collect.collect_info meta lam in
+  let lam =
+    let lam =
+      lam |> d "flatten1" |> Lam_pass_exits.simplify_exits |> d "simplify_exits"
+      |> (fun lam ->
+      Lam_pass_collect.collect_info meta lam;
+      if debug_ir then
+        Ext_log.dwarn ~__POS__ "Before simplify_alias: %a@." Lam_stats.print
+          meta;
+      lam)
+      |> Lam_pass_remove_alias.simplify_alias meta
+      |> d "simplify_alias" |> Lam_pass_deep_flatten.deep_flatten
+      |> d "flatten2"
+    in
+    (* Inling happens*)
+
+    let () = Lam_pass_collect.collect_info meta lam in
+    let lam = Lam_pass_remove_alias.simplify_alias meta lam in
+    let lam = Lam_pass_deep_flatten.deep_flatten lam in
+    let () = Lam_pass_collect.collect_info meta lam in
+    let lam =
+      lam |> d "alpha_before"
+      |> Lam_pass_alpha_conversion.alpha_conversion meta
+      |> d "alpha_after" |> Lam_pass_exits.simplify_exits
+    in
+    let () = Lam_pass_collect.collect_info meta lam in
+
+    lam |> d "simplify_alias_before"
+    |> Lam_pass_remove_alias.simplify_alias meta
+    |> d "alpha_conversion"
+    |> Lam_pass_alpha_conversion.alpha_conversion meta
+    |> d "before-simplify_lets"
+    (* we should investigate a better way to put different passes : )*)
+    |> Lam_pass_lets_dce.simplify_lets
+    |> d "before-simplify-exits"
+    (* |> (fun lam -> Lam_pass_collect.collect_info meta lam
+       ; Lam_pass_remove_alias.simplify_alias meta lam) *)
+    (* |> Lam_group_pass.scc_pass
+       |> d "scc" *)
+    |> Lam_pass_exits.simplify_exits
+    |> d "simplify_lets"
+    |> fun lam ->
+    if debug_ir then
+      Ext_log.dwarn ~__POS__ "Before coercion: %a@." Lam_stats.print meta;
+    lam
+  in
+
+  let ({Lam_coercion.groups} as coerced_input), meta =
+    Lam_coercion.coerce_and_group_big_lambda meta lam
+  in
+
+  let () =
+    if debug_ir then (
+      Ext_log.dwarn ~__POS__ "After coercion: %a@." Lam_stats.print meta;
+      Ext_option.iter diagnostics (fun diagnostics ->
+          Ir_diagnostics.dump_groups diagnostics coerced_input.groups))
+  in
+  let maybe_pure = no_side_effects groups in
+  let () =
+    if debug_ir then
+      Ext_log.dwarn ~__POS__ "\n@[[TIME:]Pre-compile: %f@]@."
+        (Sys.time () *. 1000.)
+  in
+  let body =
+    Ext_list.map groups (fun group -> compile_group output_prefix meta group)
+    |> Js_output.concat |> Js_output.output_as_block
+  in
+  let () =
+    if debug_ir then
+      Ext_log.dwarn ~__POS__ "\n@[[TIME:]Post-compile: %f@]@."
+        (Sys.time () *. 1000.)
+  in
+  (* The file is not big at all compared with [cmo] *)
+  (* Ext_marshal.to_file (Ext_path.chop_extension filename ^ ".mj")  js; *)
+  let meta_exports = meta.exports in
+  let export_set = Set_ident.of_list meta_exports in
+  let js : J.program = {exports = meta_exports; export_set; block = body} in
+  js |> j "initial" |> Js_pass_flatten.program |> j "flatten"
+  |> Js_pass_external_shadow.program |> j "external_shadow"
+  |> Js_pass_tailcall_inline.tailcall_inline |> j "inline_and_shake"
+  |> Js_pass_record_rest.program |> j "record_rest"
+  |> Js_pass_flatten_and_mark_dead.program |> j "flatten_and_mark_dead"
+  (* |> Js_inline_and_eliminate.inline_and_shake *)
+  (* |> j "inline_and_shake" *)
+  |> (fun js ->
+  ignore @@ Js_pass_scope.program js;
+  js)
+  |> Js_shake.shake_program |> j "shake"
+  |> fun (program : J.program) ->
+  let external_module_ids : Lam_module_ident.t list =
+    if !Js_config.all_module_aliases then []
+    else
+      let hard_deps = Js_fold_basic.calculate_hard_dependencies program.block in
+      Lam_compile_env.populate_required_modules may_required_modules hard_deps;
+      Ext_list.sort_via_array (Lam_module_ident.Hash_set.to_list hard_deps)
+        (fun id1 id2 ->
+          Ext_string.compare
+            (Lam_module_ident.name id1)
+            (Lam_module_ident.name id2))
+  in
+  Warnings.check_fatal ();
+  let effect_ =
+    Lam_stats_export.get_dependent_module_effect maybe_pure external_module_ids
+  in
+  let v : Js_cmj_format.t =
+    Lam_stats_export.export_to_cmj meta effect_ coerced_input.export_map
+      (if Ext_char.is_lower_case (Filename.basename output_prefix).[0] then
+         Little
+       else Upper)
+  in
+  if not !Clflags.dont_write_files then
+    Js_cmj_format.to_file ~check_exists:(not !Js_config.force_cmj)
+      (output_prefix ^ Literals.suffix_cmj)
+      v;
+  {J.program; side_effect = effect_; modules = external_module_ids}
+
+let ( // ) = Filename.concat
+
+let remove_stale_source_map ?(remove_stale_map = true) target_file =
+  if remove_stale_map && not !Clflags.dont_write_files then
+    Misc.remove_file (target_file ^ ".map")
+
+let dump_deps_program_with_source_map ?(remove_stale_map = true) ~target_file
+    ~output_prefix module_system lambda_output chan =
+  let builder =
+    Js_source_map.make ~generated_file:target_file
+      ~source_root:!Js_config.source_map_root
+      ~sources_content:!Js_config.source_map_sources_content
+  in
+  Js_source_map.with_builder builder (fun () ->
+      Js_dump_program.pp_deps_program ~output_prefix module_system lambda_output
+        (Ext_pp.from_channel chan));
+  match !Js_config.source_map with
+  | Linked ->
+    let json = Js_source_map.json builder in
+    output_string chan
+      (Js_source_map.linked_comment ~map_file:(target_file ^ ".map"));
+    Ext_io.write_file (target_file ^ ".map") json
+  | Hidden ->
+    Ext_io.write_file (target_file ^ ".map") (Js_source_map.json builder)
+  | Inline ->
+    output_string chan
+      (Js_source_map.inline_comment ~json:(Js_source_map.json builder));
+    remove_stale_source_map ~remove_stale_map target_file
+  | No_source_map -> ()
+
+let lambda_as_module (lambda_output : J.deps_program) (output_prefix : string) :
+    unit =
+  let package_info = Js_packages_state.get_packages_info () in
+  if Js_packages_info.is_empty package_info && !Js_config.js_stdout then
+    match !Js_config.source_map with
+    | Inline ->
+      let target_file =
+        Ext_namespace.change_ext_ns_suffix
+          (Filename.basename output_prefix)
+          Literals.suffix_js
+      in
+      dump_deps_program_with_source_map ~remove_stale_map:false ~target_file
+        ~output_prefix Commonjs lambda_output stdout
+    | _ ->
+      Js_dump_program.dump_deps_program ~output_prefix Commonjs lambda_output
+        stdout
+  else
+    Js_packages_info.iter package_info (fun {module_system; path; suffix} ->
+        let basename =
+          Ext_namespace.change_ext_ns_suffix
+            (Filename.basename output_prefix)
+            suffix
+        in
+        let target_file =
+          Ext_path.package_dir () // path
+          // basename (* #913 only generate little-case js file *)
+        in
+        let output_chan chan =
+          match !Js_config.source_map with
+          | No_source_map ->
+            Js_dump_program.dump_deps_program ~output_prefix module_system
+              lambda_output chan;
+            remove_stale_source_map target_file
+          | Linked | Inline | Hidden ->
+            dump_deps_program_with_source_map ~target_file ~output_prefix
+              module_system lambda_output chan
+        in
+        if not !Clflags.dont_write_files then
+          Ext_pervasives.with_file_as_chan target_file output_chan;
+        if !Warnings.has_warnings then (
+          Warnings.has_warnings := false;
+          (* 5206: When there were warnings found during the compilation, we want the file
+             to be rebuilt on the next "rescript build" so that the warnings keep being shown.
+             Set the timestamp of the ast file to 1970-01-01 to make this rebuild happen.
+             (Do *not* set the timestamp of the JS output file instead
+             as that does not play well with every bundler.) *)
+          let ast_file = output_prefix ^ Literals.suffix_ast in
+          if Sys.file_exists ast_file then Build_artifact.mark_stale ast_file))
+
+(* We can use {!Env.current_unit = "Pervasives"} to tell if it is some specific module,
+    We need handle some definitions in standard libraries in a special way, most are io specific,
+    includes {!Pervasives.stdin, Pervasives.stdout, Pervasives.stderr}
+
+    However, use filename instead of {!Env.current_unit} is more honest, since node-js module system is coupled with the file name
+*)
diff --git a/compiler/core/lam_module_ident.ml b/compiler/core/lam_module_ident.ml
index e92cdb4db0d..4ad1f1e9084 100644
--- a/compiler/core/lam_module_ident.ml
+++ b/compiler/core/lam_module_ident.ml
@@ -64,10 +64,10 @@ module Cmp = struct
     match x.kind with
     | External {name = x_kind; _} ->
       (* The hash collision is rare? *)
-      Bs_hash_stubs.hash_string x_kind
+      Ext_platform_primitives.hash_string x_kind
     | Ml | Runtime ->
       let x_id = x.id in
-      Bs_hash_stubs.hash_stamp_and_name x_id.stamp x_id.name
+      Ext_platform_primitives.hash_stamp_and_name x_id.stamp x_id.name
 end
 
 module Hash = Hash.Make (Cmp)
diff --git a/compiler/core/platform/native/build_artifact.ml b/compiler/core/platform/native/build_artifact.ml
new file mode 100644
index 00000000000..443d1c801ec
--- /dev/null
+++ b/compiler/core/platform/native/build_artifact.ml
@@ -0,0 +1,2 @@
+(* Mark an AST stale so the build system reports its warnings again. *)
+external mark_stale : string -> unit = "caml_stale_file"
diff --git a/compiler/core/platform/native/js_name_of_module_id.ml b/compiler/core/platform/native/js_name_of_module_id.ml
new file mode 100644
index 00000000000..f75abeba808
--- /dev/null
+++ b/compiler/core/platform/native/js_name_of_module_id.ml
@@ -0,0 +1,139 @@
+(* Copyright (C) 2017 Hongbo Zhang, Authors of ReScript
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * In addition to the permissions granted to you by the LGPL, you may combine
+ * or link a "work that uses the Library" with a publicly distributed version
+ * of this file to produce a combined library or application, then distribute
+ * that combined work under the terms of your choosing, with no requirement
+ * to comply with the obligations normally placed on you by section 4 of the
+ * LGPL version 3 (or the corresponding section of a later version of the LGPL
+ * should you choose to use a later version).
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * 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. *)
+
+(* Native compiler module-path resolution. *)
+(*
+let (=)  (x : int) (y:float) = assert false
+*)
+
+let ( // ) = Filename.concat
+
+let fix_path_for_windows : string -> string =
+  if Ext_sys.is_windows_or_cygwin then Ext_string.replace_backward_slash
+  else fun s -> s
+
+let runtime_suffix_of_module_system
+    (module_system : Js_packages_info.module_system) =
+  match module_system with
+  | Commonjs -> ".cjs"
+  | Esmodule -> ".mjs"
+
+(* dependency is runtime module *)
+let get_runtime_module_path (dep_module_id : Lam_module_ident.t)
+    (current_package_info : Js_packages_info.t)
+    (module_system : Js_packages_info.module_system) =
+  let current_info_query =
+    Js_packages_info.query_package_infos current_package_info module_system
+  in
+  let js_file =
+    Ext_namespace.js_name_of_modulename dep_module_id.id.name Upper
+      (runtime_suffix_of_module_system module_system)
+  in
+  match current_info_query with
+  | Package_not_found -> assert false
+  | Package_script ->
+    Js_packages_info.runtime_package_path module_system js_file
+  | Package_found pkg ->
+    let dep_path =
+      "lib" // Js_packages_info.runtime_dir_of_module_system module_system
+    in
+    if Js_packages_info.is_runtime_package current_package_info then
+      Ext_path.node_rebase_file ~from:pkg.rel_path ~to_:dep_path js_file
+      (* TODO: we assume that both [x] and [path] could only be relative path
+            which is guaranteed by [-bs-package-output]
+        *)
+    else Js_packages_info.runtime_package_path module_system js_file
+
+(* [output_dir] is decided by the command line argument *)
+let string_of_module_id (dep_module_id : Lam_module_ident.t)
+    ~(output_dir : string) (module_system : Js_packages_info.module_system) :
+    string =
+  let current_package_info = Js_packages_state.get_packages_info () in
+  fix_path_for_windows
+    (match dep_module_id.kind with
+    | External {name} -> name (* the literal string for external package *)
+    (* This may not be enough,
+        1. For cross packages, we may need settle
+        down a single js package
+        2. We may need es6 path for dead code elimination
+         But frankly, very few JS packages have no dependency,
+         so having plugin may sound not that bad
+    *)
+    | Runtime ->
+      get_runtime_module_path dep_module_id current_package_info module_system
+    | Ml -> (
+      let current_info_query =
+        Js_packages_info.query_package_infos current_package_info module_system
+      in
+      match Lam_compile_env.get_package_path_from_cmj dep_module_id with
+      | package_path, dep_package_info, case -> (
+        let dep_info_query =
+          Js_packages_info.query_package_infos dep_package_info module_system
+        in
+        match (dep_info_query, current_info_query) with
+        | Package_not_found, _ ->
+          Bs_exception.error (Missing_ml_dependency dep_module_id.id.name)
+        | Package_script, Package_found _ ->
+          Bs_exception.error
+            (Dependency_script_module_dependent_not dep_module_id.id.name)
+        | (Package_script | Package_found _), Package_not_found -> assert false
+        | Package_found ({suffix} as pkg), Package_script ->
+          let js_file =
+            Ext_namespace.js_name_of_modulename dep_module_id.id.name case
+              suffix
+          in
+          pkg.pkg_rel_path // js_file
+        | Package_found ({suffix} as dep_pkg), Package_found cur_pkg ->
+          let js_file =
+            Ext_namespace.js_name_of_modulename dep_module_id.id.name case
+              suffix
+          in
+
+          if
+            Js_packages_info.same_package_by_name current_package_info
+              dep_package_info
+          then
+            Ext_path.node_rebase_file ~from:cur_pkg.rel_path
+              ~to_:dep_pkg.rel_path js_file
+            (* TODO: we assume that both [x] and [path] could only be relative path
+                  which is guaranteed by [-bs-package-output]
+              *)
+          else if Js_packages_info.is_runtime_package dep_package_info then
+            get_runtime_module_path dep_module_id current_package_info
+              module_system
+          else dep_pkg.pkg_rel_path // js_file
+        | Package_script, Package_script -> (
+          let js_file =
+            Ext_namespace.js_name_of_modulename dep_module_id.id.name case
+              Literals.suffix_js
+          in
+          match Config_util.find_opt js_file with
+          | Some file ->
+            let basename = Filename.basename file in
+            let dirname = Filename.dirname file in
+            Ext_path.node_rebase_file
+              ~from:(Ext_path.absolute_cwd_path output_dir)
+              ~to_:(Ext_path.absolute_cwd_path dirname)
+              basename
+          | None -> Bs_exception.error (Js_not_found js_file)))))
diff --git a/compiler/core/platform/playground/build_artifact.ml b/compiler/core/platform/playground/build_artifact.ml
new file mode 100644
index 00000000000..819e7adac0e
--- /dev/null
+++ b/compiler/core/platform/playground/build_artifact.ml
@@ -0,0 +1,2 @@
+(* The playground compiler does not write build artifacts. *)
+let mark_stale _path = ()
diff --git a/compiler/core/platform/playground/js_name_of_module_id.ml b/compiler/core/platform/playground/js_name_of_module_id.ml
new file mode 100644
index 00000000000..011b3ac5f37
--- /dev/null
+++ b/compiler/core/platform/playground/js_name_of_module_id.ml
@@ -0,0 +1,6 @@
+(* The playground bundle keeps runtime modules under ./stdlib. *)
+let string_of_module_id (module_id : Lam_module_ident.t)
+    ~output_dir:(_ : string) (_module_system : Js_packages_info.module_system) =
+  match module_id.kind with
+  | External {name} -> name
+  | Runtime | Ml -> "./stdlib/" ^ module_id.id.name ^ ".mjs"
diff --git a/compiler/dune b/compiler/dune
index c56cb09eadf..dd56eeb2ce5 100644
--- a/compiler/dune
+++ b/compiler/dune
@@ -13,20 +13,11 @@
 
 (env
  (release
-  (env-vars
-   (CPPO_FLAGS -U=BROWSER))
   (ocamlopt_flags
    (:standard -O3 -unbox-closures)))
  (static
-  (env-vars
-   (CPPO_FLAGS -U=BROWSER))
   (ocamlopt_flags
    (:standard -O3 -unbox-closures)))
  (browser
-  (env-vars
-   (CPPO_FLAGS -D=BROWSER))
   (ocamlopt_flags
-   (:standard -O3 -unbox-closures)))
- (_
-  (env-vars
-   (CPPO_FLAGS -U=BROWSER))))
+   (:standard -O3 -unbox-closures))))
diff --git a/compiler/ext/bs_hash_stubs.cppo.ml b/compiler/ext/bs_hash_stubs.cppo.ml
deleted file mode 100644
index 6a59fe51ec5..00000000000
--- a/compiler/ext/bs_hash_stubs.cppo.ml
+++ /dev/null
@@ -1,40 +0,0 @@
-
-#ifdef BROWSER 
-
-
-let hash_string : string -> int = Hashtbl.hash
-let hash_string_int s i = Hashtbl.hash (s,i)
-let hash_string_small_int :  string -> int  -> int = hash_string_int
-let hash_stamp_and_name (i:int) (s:string) = Hashtbl.hash(i,s)
-let hash_int (i:int) = Hashtbl.hash i 
-let string_length_based_compare (x : string ) (y : string) = 
-  let len1 = String.length x in 
-  let len2 = String.length y in 
-  if len1 = len2 then String.compare x y 
-  else compare (len1:int) len2
-let int_unsafe_blit: int array -> int -> int array -> int -> int -> unit = 
-  Array.blit
-
-#else
-external hash_string :  string -> int = "caml_bs_hash_string" [@@noalloc];;
-
-external hash_string_int :  string -> int  -> int = "caml_bs_hash_string_and_int" [@@noalloc];;
-
-external hash_string_small_int :  string -> int  -> int = "caml_bs_hash_string_and_small_int" [@@noalloc];;
-
-external hash_stamp_and_name : int -> string -> int = "caml_bs_hash_stamp_and_name" [@@noalloc];;
-
-external hash_small_int : int -> int = "caml_bs_hash_small_int" [@@noalloc];;
-
-external hash_int :  int  -> int = "caml_bs_hash_int" [@@noalloc];;
-
-external string_length_based_compare : string -> string -> int  = "caml_string_length_based_compare" [@@noalloc];;
-
-external    
-  int_unsafe_blit : 
-  int array -> int -> int array -> int -> int -> unit = "caml_int_array_blit" [@@noalloc];;
-
-external set_as_old_file : string -> unit = "caml_stale_file"
-#endif
-
-
diff --git a/compiler/ext/dune b/compiler/ext/dune
index c6a8a9dfeb9..e8379a964c5 100644
--- a/compiler/ext/dune
+++ b/compiler/ext/dune
@@ -1,50 +1,36 @@
-(library
- (name ext)
- (wrapped false)
- (instrumentation
-  (backend bisect_ppx))
- (flags
-  (:standard -w +a-4-42-40-9-48-70))
- (foreign_stubs
-  (language c)
-  (names ext_basic_hash_stubs)))
+(env
+ (_
+  (flags
+   (:standard -w +a-4-42-40-9-48-70))))
 
-(rule
- (target bs_hash_stubs.ml)
- (deps bs_hash_stubs.cppo.ml)
- (action
-  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+; The browser profile builds the playground compiler; this rule pair generates a module from platform/{native,playground}.
 
 (rule
- (target js_reserved_map.ml)
- (deps js_reserved_map.cppo.ml)
+ (target ext_platform_primitives.ml)
+ (enabled_if
+  (= %{profile} browser))
  (action
-  (run
-   %{bin:cppo}
-   -V
-   OCAML:%{ocaml_version}
-   %{env:CPPO_FLAGS=}
-   %{deps}
-   -o
-   %{target})))
+  (copy
+   platform/playground/ext_platform_primitives.ml
+   ext_platform_primitives.ml)))
 
 (rule
- (target ext_sys.ml)
- (deps ext_sys.cppo.ml)
+ (target ext_platform_primitives.ml)
+ (enabled_if
+  (<> %{profile} browser))
  (action
-  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+  (copy
+   platform/native/ext_platform_primitives.ml
+   ext_platform_primitives.ml)))
 
-(rule
- (target ext_string.ml)
- (deps ext_string.cppo.ml)
- (action
-  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
-
-(rule
- (target ext_string.mli)
- (deps ext_string.cppo.mli)
- (action
-  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
+(library
+ (name ext)
+ (wrapped false)
+ (instrumentation
+  (backend bisect_ppx))
+ (foreign_stubs
+  (language c)
+  (names ext_platform_primitives_stubs)))
 
 (rule
  (targets hash_set_string.ml)
diff --git a/compiler/ext/ext_basic_hash_stubs.c b/compiler/ext/ext_platform_primitives_stubs.c
similarity index 59%
rename from compiler/ext/ext_basic_hash_stubs.c
rename to compiler/ext/ext_platform_primitives_stubs.c
index 4937997fecd..b1f32eb63d2 100644
--- a/compiler/ext/ext_basic_hash_stubs.c
+++ b/compiler/ext/ext_platform_primitives_stubs.c
@@ -1,12 +1,8 @@
 #include "caml/hash.h"
 #include "caml/mlvalues.h"
-#include <string.h>
 #include <stdint.h>
-#include "caml/memory.h"
-#include "caml/osdeps.h"
-#include "caml/signals.h"
+#include <string.h>
 #include "caml/misc.h"
-#include <sys/stat.h>
 typedef uint32_t uint32;
 
 #define FINAL_MIX(h) \
@@ -49,23 +45,6 @@ CAMLprim value caml_bs_hash_string_and_int  (value obj, value d){
   return Val_int(h & 0x3FFFFFFFU);
 }
 
-CAMLprim value caml_bs_hash_string_and_small_int(value obj, value d){
-  uint32 h = 0;
-  h = caml_hash_mix_string(h,obj);
-  MIX(h,d);
-  FINAL_MIX(h);
-  return Val_int(h & 0x3FFFFFFFU);
-}
-
-CAMLprim value caml_bs_hash_small_int(value d){
-  uint32 h = 0; 
-  // intnat stamp = Long_val(d); 
-  // FIXME: unused value
-  MIX(h,d);
-  FINAL_MIX(h);
-  return Val_int(h & 0x3FFFFFFFU);
-}
-
 CAMLprim value caml_int_array_blit(
   value a1, value ofs1, 
   value a2, value ofs2,
@@ -142,75 +121,6 @@ CAMLprim value caml_string_length_based_compare(value s1, value s2)
 
 
 
-#include <sys/time.h>
-#ifdef _WIN32
-#include <sys/utime.h>
-CAMLprim value caml_stale_file(value path)
-{
-  CAMLparam1(path);
-  struct _utimbuf tv;
-  char * p = caml_stat_strdup(String_val(path));
-  tv.modtime = 0;  
-  caml_enter_blocking_section();
-  _utime(p, &tv);
-  caml_leave_blocking_section();
-  caml_stat_free(p);
-  CAMLreturn(Val_unit);
-}
-#else
-CAMLprim value caml_stale_file(value path)
-{
-  CAMLparam1(path);
-  struct timeval tv[2];
-  char * p = caml_stat_strdup_to_os(String_val(path));
-  // unicode friendly
-  tv[0].tv_sec = 0.0;
-  tv[0].tv_usec = 0.0;
-  tv[1].tv_sec = 0.0;
-  tv[1].tv_usec = 0.0;
-  // caml_enter_blocking_section();
-  // not needed for single thread
-  utimes(p, tv);
-  // caml_leave_blocking_section();
-  // not needed for single thread
-  caml_stat_free(p);
-  // TODO: error checking
-  CAMLreturn(Val_unit);
-}
-#endif
-
-
-CAMLprim value caml_sys_is_directory_no_exn(value name)
-{
-  CAMLparam1(name);
-#ifdef _WIN32
-  struct _stati64 st;
-#else
-  struct stat st;
-#endif
-  char_os * p;
-  int ret;
-
-  
-  if(!caml_string_is_c_safe(name)){
-    CAMLreturn(Val_false);
-  }
-
-  p = caml_stat_strdup_to_os(String_val(name));
-  caml_enter_blocking_section();
-  ret = stat_os(p, &st);
-  caml_leave_blocking_section();
-  caml_stat_free(p);
-
-  if (ret == -1) CAMLreturn(Val_false);
-#ifdef S_ISDIR
-  CAMLreturn(Val_bool(S_ISDIR(st.st_mode)));
-#else
-  CAMLreturn(Val_bool(st.st_mode & S_IFDIR));
-#endif
-}
 /* local variables: */
-/* compile-command: "ocamlopt.opt -c ext_basic_hash_stubs.c" */
+/* compile-command: "ocamlopt.opt -c ext_platform_primitives_stubs.c" */
 /* end: */
-
-
diff --git a/compiler/ext/ext_string.cppo.ml b/compiler/ext/ext_string.cppo.ml
deleted file mode 100644
index dcc7ab00e40..00000000000
--- a/compiler/ext/ext_string.cppo.ml
+++ /dev/null
@@ -1,530 +0,0 @@
-(* Copyright (C) 2015 - 2016 Bloomberg Finance L.P.
- * Copyright (C) 2017 - Hongbo Zhang, Authors of ReScript
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU Lesser General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * In addition to the permissions granted to you by the LGPL, you may combine
- * or link a "work that uses the Library" with a publicly distributed version
- * of this file to produce a combined library or application, then distribute
- * that combined work under the terms of your choosing, with no requirement
- * to comply with the obligations normally placed on you by section 4 of the
- * LGPL version 3 (or the corresponding section of a later version of the LGPL
- * should you choose to use a later version).
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU Lesser General Public License for more details.
- * 
- * 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. *)
-
-
-
-
-
-
-
-(*
-   {[ split " test_unsafe_obj_ffi_ppx.cmi" ~keep_empty:false ' ']}
-*)
-let split_by ?(keep_empty=false) is_delim str =
-  let len = String.length str in
-  let rec loop acc last_pos pos =
-    if pos = -1 then
-      if last_pos = 0 && not keep_empty then
-
-        acc
-      else 
-        String.sub str 0 last_pos :: acc
-    else
-    if is_delim str.[pos] then
-      let new_len = (last_pos - pos - 1) in
-      if new_len <> 0 || keep_empty then 
-        let v = String.sub str (pos + 1) new_len in
-        loop ( v :: acc)
-          pos (pos - 1)
-      else loop acc pos (pos - 1)
-    else loop acc last_pos (pos - 1)
-  in
-  loop [] len (len - 1)
-
-let trim s = 
-  let i = ref 0  in
-  let j = String.length s in 
-  while !i < j &&  
-        let u = String.unsafe_get s !i in 
-        u = '\t' || u = '\n' || u = ' ' 
-  do 
-    incr i;
-  done;
-  let k = ref (j - 1)  in 
-  while !k >= !i && 
-        let u = String.unsafe_get s !k in 
-        u = '\t' || u = '\n' || u = ' ' do 
-    decr k ;
-  done;
-  String.sub s !i (!k - !i + 1)
-
-let split ?keep_empty  str on = 
-  if str = "" then [] else 
-    split_by ?keep_empty (fun x -> (x : char) = on) str  ;;
-
-let quick_split_by_ws str : string list = 
-  split_by ~keep_empty:false (fun x -> x = '\t' || x = '\n' || x = ' ') str
-
-let starts_with s beg = 
-  let beg_len = String.length beg in
-  let s_len = String.length s in
-  beg_len <=  s_len &&
-  (let i = ref 0 in
-   while !i <  beg_len 
-         && String.unsafe_get s !i =
-            String.unsafe_get beg !i do 
-     incr i 
-   done;
-   !i = beg_len
-  )
-
-let rec ends_aux s end_ j k = 
-  if k < 0 then (j + 1)
-  else if String.unsafe_get s j = String.unsafe_get end_ k then 
-    ends_aux s end_ (j - 1) (k - 1)
-  else  -1   
-
-(** return an index which is minus when [s] does not 
-    end with [beg]
-*)
-let ends_with_index s end_ : int = 
-  let s_finish = String.length s - 1 in
-  let s_beg = String.length end_ - 1 in
-  if s_beg > s_finish then -1
-  else
-    ends_aux s end_ s_finish s_beg
-
-let ends_with s end_ = ends_with_index s end_ >= 0 
-
-let ends_with_then_chop s beg = 
-  let i =  ends_with_index s beg in 
-  if i >= 0 then Some (String.sub s 0 i) 
-  else None
-
-(* let check_suffix_case = ends_with  *)
-(* let check_suffix_case_then_chop = ends_with_then_chop *)
-
-(* let check_any_suffix_case s suffixes = 
-   Ext_list.exists suffixes (fun x -> check_suffix_case s x)  *)
-
-(* let check_any_suffix_case_then_chop s suffixes = 
-   let rec aux suffixes = 
-    match suffixes with 
-    | [] -> None 
-    | x::xs -> 
-      let id = ends_with_index s x in 
-      if id >= 0 then Some (String.sub s 0 id)
-      else aux xs in 
-   aux suffixes     *)
-
-
-
-
-(* it is unsafe to expose such API as unsafe since 
-   user can provide bad input range 
-
-*)
-let rec unsafe_for_all_range s ~start ~finish p =     
-  start > finish ||
-  p (String.unsafe_get s start) && 
-  unsafe_for_all_range s ~start:(start + 1) ~finish p
-
-let for_all_from s start  p = 
-  let len = String.length s in 
-  if start < 0  then invalid_arg "Ext_string.for_all_from"
-  else unsafe_for_all_range s ~start ~finish:(len - 1) p 
-
-
-let for_all s (p : char -> bool)  =   
-  unsafe_for_all_range s ~start:0  ~finish:(String.length s - 1) p 
-
-let is_empty s = String.length s = 0
-
-
-let repeat n s  =
-  let len = String.length s in
-  let res = Bytes.create(n * len) in
-  for i = 0 to pred n do
-    String.blit s 0 res (i * len) len
-  done;
-  Bytes.to_string res
-
-
-
-
-let unsafe_is_sub ~sub i s j ~len =
-  let rec check k =
-    if k = len
-    then true
-    else 
-      String.unsafe_get sub (i+k) = 
-      String.unsafe_get s (j+k) && check (k+1)
-  in
-  j+len <= String.length s && check 0
-
-
-
-let find ?(start=0) ~sub s =
-  let exception Local_exit in
-  let n = String.length sub in
-  let s_len = String.length s in 
-  let i = ref start in  
-  try
-    while !i + n <= s_len do
-      if unsafe_is_sub ~sub 0 s !i ~len:n then
-        raise_notrace Local_exit;
-      incr i
-    done;
-    -1
-  with Local_exit ->
-    !i
-
-let contain_substring s sub = 
-  find s ~sub >= 0 
-
-(** TODO: optimize 
-    avoid nonterminating when string is empty 
-*)
-let non_overlap_count ~sub s = 
-  let sub_len = String.length sub in 
-  let rec aux  acc off = 
-    let i = find ~start:off ~sub s  in 
-    if i < 0 then acc 
-    else aux (acc + 1) (i + sub_len) in
-  if String.length sub = 0 then invalid_arg "Ext_string.non_overlap_count"
-  else aux 0 0  
-
-
-let rfind ~sub s =
-  let exception Local_exit in   
-  let n = String.length sub in
-  let i = ref (String.length s - n) in
-  try
-    while !i >= 0 do
-      if unsafe_is_sub ~sub 0 s !i ~len:n then 
-        raise_notrace Local_exit;
-      decr i
-    done;
-    -1
-  with Local_exit ->
-    !i
-
-let tail_from s x = 
-  let len = String.length s  in 
-  if  x > len then invalid_arg ("Ext_string.tail_from " ^s ^ " : "^ string_of_int x )
-  else String.sub s x (len - x)
-
-let equal (x : string) y  = x = y
-
-(* let rec index_rec s lim i c =
-   if i >= lim then -1 else
-   if String.unsafe_get s i = c then i 
-   else index_rec s lim (i + 1) c *)
-
-
-
-let rec index_rec_count s lim i c count =
-  if i >= lim then -1 else
-  if String.unsafe_get s i = c then 
-    if count = 1 then i 
-    else index_rec_count s lim (i + 1) c (count - 1)
-  else index_rec_count s lim (i + 1) c count
-
-let index_count s i c count =     
-  let lim = String.length s in 
-  if i < 0 || i >= lim || count < 1 then 
-    invalid_arg ("index_count: ( " ^string_of_int i ^ "," ^string_of_int count ^ ")" );
-  index_rec_count s lim i c count 
-
-(* let index_next s i c =   
-   index_count s i c 1  *)
-
-(* let extract_until s cursor c =       
-   let len = String.length s in   
-   let start = !cursor in 
-   if start < 0 || start >= len then (
-    cursor := -1;
-    ""
-    )
-   else 
-    let i = index_rec s len start c in   
-    let finish = 
-      if i < 0 then (      
-        cursor := -1 ;
-        len 
-      )
-      else (
-        cursor := i + 1;
-        i 
-      ) in 
-    String.sub s start (finish - start) *)
-
-let rec rindex_rec s i c =
-  if i < 0 then i else
-  if String.unsafe_get s i = c then i else rindex_rec s (i - 1) c;;
-
-let rec rindex_rec_opt s i c =
-  if i < 0 then None else
-  if String.unsafe_get s i = c then Some i else rindex_rec_opt s (i - 1) c;;
-
-let rindex_neg s c = 
-  rindex_rec s (String.length s - 1) c;;
-
-let rindex_opt s c = 
-  rindex_rec_opt s (String.length s - 1) c;;
-
-
-(** TODO: can be improved to return a positive integer instead *)
-let rec unsafe_no_char x ch i  last_idx = 
-  i > last_idx  || 
-  (String.unsafe_get x i <> ch && unsafe_no_char x ch (i + 1)  last_idx)
-
-let rec unsafe_no_char_idx x ch i last_idx = 
-  if i > last_idx  then -1 
-  else 
-  if String.unsafe_get x i <> ch then 
-    unsafe_no_char_idx x ch (i + 1)  last_idx
-  else i
-
-let no_char x ch i len  : bool =
-  let str_len = String.length x in 
-  if i < 0 || i >= str_len || len >= str_len then invalid_arg "Ext_string.no_char"   
-  else unsafe_no_char x ch i len 
-
-
-let no_slash x = 
-  unsafe_no_char x '/' 0 (String.length x - 1)
-
-let no_slash_idx x = 
-  unsafe_no_char_idx x '/' 0 (String.length x - 1)
-
-let no_slash_idx_from x from = 
-  let last_idx = String.length x - 1  in 
-  assert (from >= 0); 
-  unsafe_no_char_idx x '/' from last_idx
-
-let replace_slash_backward (x : string ) = 
-  let len = String.length x in 
-  if unsafe_no_char x '/' 0  (len - 1) then x 
-  else 
-    String.map (function 
-        | '/' -> '\\'
-        | x -> x ) x 
-
-let replace_backward_slash (x : string)=
-  let len = String.length x in
-  if unsafe_no_char x '\\' 0  (len -1) then x 
-  else  
-    String.map (function 
-        |'\\'-> '/'
-        | x -> x) x
-
-let empty = ""
-
-#ifdef BROWSER 
-let compare = Bs_hash_stubs.string_length_based_compare
-#else
-external compare : string -> string -> int = "caml_string_length_based_compare" [@@noalloc];;    
-#endif
-let single_space = " "
-let single_colon = ":"
-
-let concat_array sep (s : string array) =   
-  let s_len = Array.length s in 
-  match s_len with 
-  | 0 -> empty 
-  | 1 -> Array.unsafe_get s 0
-  | _ ->     
-    let sep_len = String.length sep in 
-    let len = ref 0 in 
-    for i = 0 to  s_len - 1 do 
-      len := !len + String.length (Array.unsafe_get s i)
-    done;
-    let target = 
-      Bytes.create 
-        (!len + (s_len - 1) * sep_len ) in    
-    let hd = (Array.unsafe_get s 0) in     
-    let hd_len = String.length hd in 
-    String.unsafe_blit hd  0  target 0 hd_len;   
-    let current_offset = ref hd_len in     
-    for i = 1 to s_len - 1 do 
-      String.unsafe_blit sep 0 target  !current_offset sep_len;
-      let cur = Array.unsafe_get s i in 
-      let cur_len = String.length cur in     
-      let new_off_set = (!current_offset + sep_len ) in
-      String.unsafe_blit cur 0 target new_off_set cur_len; 
-      current_offset := 
-        new_off_set + cur_len ; 
-    done;
-    Bytes.unsafe_to_string target   
-
-let concat3 a b c = 
-  let a_len = String.length a in 
-  let b_len = String.length b in 
-  let c_len = String.length c in 
-  let len = a_len + b_len + c_len in 
-  let target = Bytes.create len in 
-  String.unsafe_blit a 0 target 0 a_len ; 
-  String.unsafe_blit b 0 target a_len b_len;
-  String.unsafe_blit c 0 target (a_len + b_len) c_len;
-  Bytes.unsafe_to_string target
-
-let concat4 a b c d =
-  let a_len = String.length a in 
-  let b_len = String.length b in 
-  let c_len = String.length c in 
-  let d_len = String.length d in 
-  let len = a_len + b_len + c_len + d_len in 
-
-  let target = Bytes.create len in 
-  String.unsafe_blit a 0 target 0 a_len ; 
-  String.unsafe_blit b 0 target a_len b_len;
-  String.unsafe_blit c 0 target (a_len + b_len) c_len;
-  String.unsafe_blit d 0 target (a_len + b_len + c_len) d_len;
-  Bytes.unsafe_to_string target
-
-
-let concat5 a b c d e =
-  let a_len = String.length a in 
-  let b_len = String.length b in 
-  let c_len = String.length c in 
-  let d_len = String.length d in 
-  let e_len = String.length e in 
-  let len = a_len + b_len + c_len + d_len + e_len in 
-
-  let target = Bytes.create len in 
-  String.unsafe_blit a 0 target 0 a_len ; 
-  String.unsafe_blit b 0 target a_len b_len;
-  String.unsafe_blit c 0 target (a_len + b_len) c_len;
-  String.unsafe_blit d 0 target (a_len + b_len + c_len) d_len;
-  String.unsafe_blit e 0 target (a_len + b_len + c_len + d_len) e_len;
-  Bytes.unsafe_to_string target
-
-
-
-let inter2 a b = 
-  concat3 a single_space b 
-
-
-let inter3 a b c = 
-  concat5 a  single_space  b  single_space  c 
-
-
-
-
-
-let inter4 a b c d =
-  concat_array single_space [| a; b ; c; d|]
-
-
-let parent_dir_lit = ".."    
-let current_dir_lit = "."
-
-
-(* reference {!Bytes.unppercase} *)
-let capitalize_ascii (s : string) : string = 
-  if String.length s = 0 then s 
-  else 
-    begin
-      let c = String.unsafe_get s 0 in 
-      if (c >= 'a' && c <= 'z')
-      || (c >= '\224' && c <= '\246')
-      || (c >= '\248' && c <= '\254') then 
-        let uc = Char.unsafe_chr (Char.code c - 32) in 
-        let bytes = Bytes.of_string s in
-        Bytes.unsafe_set bytes 0 uc;
-        Bytes.unsafe_to_string bytes 
-      else s 
-    end
-
-let capitalize_sub (s : string) len : string = 
-  let slen = String.length s in 
-  if  len < 0 || len > slen then invalid_arg "Ext_string.capitalize_sub"
-  else 
-  if len = 0 then ""
-  else 
-    let bytes = Bytes.create len in 
-    let uc = 
-      let c = String.unsafe_get s 0 in 
-      if (c >= 'a' && c <= 'z')
-      || (c >= '\224' && c <= '\246')
-      || (c >= '\248' && c <= '\254') then 
-        Char.unsafe_chr (Char.code c - 32) else c in 
-    Bytes.unsafe_set bytes 0 uc;
-    for i = 1 to len - 1 do 
-      Bytes.unsafe_set bytes i (String.unsafe_get s i)
-    done ;
-    Bytes.unsafe_to_string bytes 
-
-
-
-let uncapitalize_ascii =
-  String.uncapitalize_ascii
-
-let lowercase_ascii = String.lowercase_ascii
-
-external (.![]) : string -> int -> int = "%string_unsafe_get"
-
-let get_int_1_unsafe (x : string) off : int = 
-  x.![off]
-
-let get_int_2_unsafe (x : string) off : int =   
-  x.![off] lor   
-  x.![off+1] lsl 8
-
-let get_int_3_unsafe (x : string) off : int = 
-  x.![off] lor   
-  x.![off+1] lsl 8  lor 
-  x.![off+2] lsl 16
-
-
-let get_int_4_unsafe (x : string) off : int =     
-  x.![off] lor   
-  x.![off+1] lsl 8  lor 
-  x.![off+2] lsl 16 lor
-  x.![off+3] lsl 24 
-
-let get_1_2_3_4 (x : string) ~off len : int =  
-  if len = 1 then get_int_1_unsafe x off 
-  else if len = 2 then get_int_2_unsafe x off 
-  else if len = 3 then get_int_3_unsafe x off 
-  else if len = 4 then get_int_4_unsafe x off 
-  else assert false
-
-let unsafe_sub  x offs len =
-  let b = Bytes.create len in 
-  Ext_bytes.unsafe_blit_string x offs b 0 len;
-  (Bytes.unsafe_to_string b)
-
-let is_valid_hash_number (x:string) = 
-  let len = String.length x in 
-  len > 0 && (
-    let a = x.![0] in 
-    a <= 57 &&
-    (if len > 1 then 
-       a > 48 && 
-       for_all_from x 1 (function '0' .. '9' -> true | _ -> false)
-     else
-       a >= 48 )
-  ) 
-
-
-let hash_number_as_i32_exn 
-    ( x : string) : int32 = 
-  Int32.of_string x    
-
-
-let first_marshal_char (x : string) = 
-    x <> ""   &&
-    ( String.unsafe_get x  0 = '\132')
diff --git a/compiler/ext/ext_string.ml b/compiler/ext/ext_string.ml
new file mode 100644
index 00000000000..ec564df90b4
--- /dev/null
+++ b/compiler/ext/ext_string.ml
@@ -0,0 +1,469 @@
+(* Copyright (C) 2015 - 2016 Bloomberg Finance L.P.
+ * Copyright (C) 2017 - Hongbo Zhang, Authors of ReScript
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * In addition to the permissions granted to you by the LGPL, you may combine
+ * or link a "work that uses the Library" with a publicly distributed version
+ * of this file to produce a combined library or application, then distribute
+ * that combined work under the terms of your choosing, with no requirement
+ * to comply with the obligations normally placed on you by section 4 of the
+ * LGPL version 3 (or the corresponding section of a later version of the LGPL
+ * should you choose to use a later version).
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * 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. *)
+
+(*
+   {[ split " test_unsafe_obj_ffi_ppx.cmi" ~keep_empty:false ' ']}
+*)
+let split_by ?(keep_empty = false) is_delim str =
+  let len = String.length str in
+  let rec loop acc last_pos pos =
+    if pos = -1 then
+      if last_pos = 0 && not keep_empty then acc
+      else String.sub str 0 last_pos :: acc
+    else if is_delim str.[pos] then
+      let new_len = last_pos - pos - 1 in
+      if new_len <> 0 || keep_empty then
+        let v = String.sub str (pos + 1) new_len in
+        loop (v :: acc) pos (pos - 1)
+      else loop acc pos (pos - 1)
+    else loop acc last_pos (pos - 1)
+  in
+  loop [] len (len - 1)
+
+let trim s =
+  let i = ref 0 in
+  let j = String.length s in
+  while
+    !i < j
+    &&
+    let u = String.unsafe_get s !i in
+    u = '\t' || u = '\n' || u = ' '
+  do
+    incr i
+  done;
+  let k = ref (j - 1) in
+  while
+    !k >= !i
+    &&
+    let u = String.unsafe_get s !k in
+    u = '\t' || u = '\n' || u = ' '
+  do
+    decr k
+  done;
+  String.sub s !i (!k - !i + 1)
+
+let split ?keep_empty str on =
+  if str = "" then [] else split_by ?keep_empty (fun x -> (x : char) = on) str
+
+let quick_split_by_ws str : string list =
+  split_by ~keep_empty:false (fun x -> x = '\t' || x = '\n' || x = ' ') str
+
+let starts_with s beg =
+  let beg_len = String.length beg in
+  let s_len = String.length s in
+  beg_len <= s_len
+  &&
+  let i = ref 0 in
+  while !i < beg_len && String.unsafe_get s !i = String.unsafe_get beg !i do
+    incr i
+  done;
+  !i = beg_len
+
+let rec ends_aux s end_ j k =
+  if k < 0 then j + 1
+  else if String.unsafe_get s j = String.unsafe_get end_ k then
+    ends_aux s end_ (j - 1) (k - 1)
+  else -1
+
+(** return an index which is minus when [s] does not
+    end with [beg]
+*)
+let ends_with_index s end_ : int =
+  let s_finish = String.length s - 1 in
+  let s_beg = String.length end_ - 1 in
+  if s_beg > s_finish then -1 else ends_aux s end_ s_finish s_beg
+
+let ends_with s end_ = ends_with_index s end_ >= 0
+
+let ends_with_then_chop s beg =
+  let i = ends_with_index s beg in
+  if i >= 0 then Some (String.sub s 0 i) else None
+
+(* let check_suffix_case = ends_with  *)
+(* let check_suffix_case_then_chop = ends_with_then_chop *)
+
+(* let check_any_suffix_case s suffixes =
+   Ext_list.exists suffixes (fun x -> check_suffix_case s x)  *)
+
+(* let check_any_suffix_case_then_chop s suffixes =
+   let rec aux suffixes =
+    match suffixes with
+    | [] -> None
+    | x::xs ->
+      let id = ends_with_index s x in
+      if id >= 0 then Some (String.sub s 0 id)
+      else aux xs in
+   aux suffixes     *)
+
+(* it is unsafe to expose such API as unsafe since
+   user can provide bad input range
+
+*)
+let rec unsafe_for_all_range s ~start ~finish p =
+  start > finish
+  || p (String.unsafe_get s start)
+     && unsafe_for_all_range s ~start:(start + 1) ~finish p
+
+let for_all_from s start p =
+  let len = String.length s in
+  if start < 0 then invalid_arg "Ext_string.for_all_from"
+  else unsafe_for_all_range s ~start ~finish:(len - 1) p
+
+let for_all s (p : char -> bool) =
+  unsafe_for_all_range s ~start:0 ~finish:(String.length s - 1) p
+
+let is_empty s = String.length s = 0
+
+let repeat n s =
+  let len = String.length s in
+  let res = Bytes.create (n * len) in
+  for i = 0 to pred n do
+    String.blit s 0 res (i * len) len
+  done;
+  Bytes.to_string res
+
+let unsafe_is_sub ~sub i s j ~len =
+  let rec check k =
+    if k = len then true
+    else
+      String.unsafe_get sub (i + k) = String.unsafe_get s (j + k)
+      && check (k + 1)
+  in
+  j + len <= String.length s && check 0
+
+let find ?(start = 0) ~sub s =
+  let exception Local_exit in
+  let n = String.length sub in
+  let s_len = String.length s in
+  let i = ref start in
+  try
+    while !i + n <= s_len do
+      if unsafe_is_sub ~sub 0 s !i ~len:n then raise_notrace Local_exit;
+      incr i
+    done;
+    -1
+  with Local_exit -> !i
+
+let contain_substring s sub = find s ~sub >= 0
+
+(** TODO: optimize
+    avoid nonterminating when string is empty
+*)
+let non_overlap_count ~sub s =
+  let sub_len = String.length sub in
+  let rec aux acc off =
+    let i = find ~start:off ~sub s in
+    if i < 0 then acc else aux (acc + 1) (i + sub_len)
+  in
+  if String.length sub = 0 then invalid_arg "Ext_string.non_overlap_count"
+  else aux 0 0
+
+let rfind ~sub s =
+  let exception Local_exit in
+  let n = String.length sub in
+  let i = ref (String.length s - n) in
+  try
+    while !i >= 0 do
+      if unsafe_is_sub ~sub 0 s !i ~len:n then raise_notrace Local_exit;
+      decr i
+    done;
+    -1
+  with Local_exit -> !i
+
+let tail_from s x =
+  let len = String.length s in
+  if x > len then
+    invalid_arg ("Ext_string.tail_from " ^ s ^ " : " ^ string_of_int x)
+  else String.sub s x (len - x)
+
+let equal (x : string) y = x = y
+
+(* let rec index_rec s lim i c =
+   if i >= lim then -1 else
+   if String.unsafe_get s i = c then i
+   else index_rec s lim (i + 1) c *)
+
+let rec index_rec_count s lim i c count =
+  if i >= lim then -1
+  else if String.unsafe_get s i = c then
+    if count = 1 then i else index_rec_count s lim (i + 1) c (count - 1)
+  else index_rec_count s lim (i + 1) c count
+
+let index_count s i c count =
+  let lim = String.length s in
+  if i < 0 || i >= lim || count < 1 then
+    invalid_arg
+      ("index_count: ( " ^ string_of_int i ^ "," ^ string_of_int count ^ ")");
+  index_rec_count s lim i c count
+
+(* let index_next s i c =
+   index_count s i c 1  *)
+
+(* let extract_until s cursor c =
+   let len = String.length s in
+   let start = !cursor in
+   if start < 0 || start >= len then (
+    cursor := -1;
+    ""
+    )
+   else
+    let i = index_rec s len start c in
+    let finish =
+      if i < 0 then (
+        cursor := -1 ;
+        len
+      )
+      else (
+        cursor := i + 1;
+        i
+      ) in
+    String.sub s start (finish - start) *)
+
+let rec rindex_rec s i c =
+  if i < 0 then i
+  else if String.unsafe_get s i = c then i
+  else rindex_rec s (i - 1) c
+
+let rec rindex_rec_opt s i c =
+  if i < 0 then None
+  else if String.unsafe_get s i = c then Some i
+  else rindex_rec_opt s (i - 1) c
+
+let rindex_neg s c = rindex_rec s (String.length s - 1) c
+
+let rindex_opt s c = rindex_rec_opt s (String.length s - 1) c
+
+(** TODO: can be improved to return a positive integer instead *)
+let rec unsafe_no_char x ch i last_idx =
+  i > last_idx
+  || (String.unsafe_get x i <> ch && unsafe_no_char x ch (i + 1) last_idx)
+
+let rec unsafe_no_char_idx x ch i last_idx =
+  if i > last_idx then -1
+  else if String.unsafe_get x i <> ch then
+    unsafe_no_char_idx x ch (i + 1) last_idx
+  else i
+
+let no_char x ch i len : bool =
+  let str_len = String.length x in
+  if i < 0 || i >= str_len || len >= str_len then
+    invalid_arg "Ext_string.no_char"
+  else unsafe_no_char x ch i len
+
+let no_slash x = unsafe_no_char x '/' 0 (String.length x - 1)
+
+let no_slash_idx x = unsafe_no_char_idx x '/' 0 (String.length x - 1)
+
+let no_slash_idx_from x from =
+  let last_idx = String.length x - 1 in
+  assert (from >= 0);
+  unsafe_no_char_idx x '/' from last_idx
+
+let replace_slash_backward (x : string) =
+  let len = String.length x in
+  if unsafe_no_char x '/' 0 (len - 1) then x
+  else
+    String.map
+      (function
+        | '/' -> '\\'
+        | x -> x)
+      x
+
+let replace_backward_slash (x : string) =
+  let len = String.length x in
+  if unsafe_no_char x '\\' 0 (len - 1) then x
+  else
+    String.map
+      (function
+        | '\\' -> '/'
+        | x -> x)
+      x
+
+let empty = ""
+
+let compare = Ext_platform_primitives.string_length_based_compare
+let single_space = " "
+let single_colon = ":"
+
+let concat_array sep (s : string array) =
+  let s_len = Array.length s in
+  match s_len with
+  | 0 -> empty
+  | 1 -> Array.unsafe_get s 0
+  | _ ->
+    let sep_len = String.length sep in
+    let len = ref 0 in
+    for i = 0 to s_len - 1 do
+      len := !len + String.length (Array.unsafe_get s i)
+    done;
+    let target = Bytes.create (!len + ((s_len - 1) * sep_len)) in
+    let hd = Array.unsafe_get s 0 in
+    let hd_len = String.length hd in
+    String.unsafe_blit hd 0 target 0 hd_len;
+    let current_offset = ref hd_len in
+    for i = 1 to s_len - 1 do
+      String.unsafe_blit sep 0 target !current_offset sep_len;
+      let cur = Array.unsafe_get s i in
+      let cur_len = String.length cur in
+      let new_off_set = !current_offset + sep_len in
+      String.unsafe_blit cur 0 target new_off_set cur_len;
+      current_offset := new_off_set + cur_len
+    done;
+    Bytes.unsafe_to_string target
+
+let concat3 a b c =
+  let a_len = String.length a in
+  let b_len = String.length b in
+  let c_len = String.length c in
+  let len = a_len + b_len + c_len in
+  let target = Bytes.create len in
+  String.unsafe_blit a 0 target 0 a_len;
+  String.unsafe_blit b 0 target a_len b_len;
+  String.unsafe_blit c 0 target (a_len + b_len) c_len;
+  Bytes.unsafe_to_string target
+
+let concat4 a b c d =
+  let a_len = String.length a in
+  let b_len = String.length b in
+  let c_len = String.length c in
+  let d_len = String.length d in
+  let len = a_len + b_len + c_len + d_len in
+
+  let target = Bytes.create len in
+  String.unsafe_blit a 0 target 0 a_len;
+  String.unsafe_blit b 0 target a_len b_len;
+  String.unsafe_blit c 0 target (a_len + b_len) c_len;
+  String.unsafe_blit d 0 target (a_len + b_len + c_len) d_len;
+  Bytes.unsafe_to_string target
+
+let concat5 a b c d e =
+  let a_len = String.length a in
+  let b_len = String.length b in
+  let c_len = String.length c in
+  let d_len = String.length d in
+  let e_len = String.length e in
+  let len = a_len + b_len + c_len + d_len + e_len in
+
+  let target = Bytes.create len in
+  String.unsafe_blit a 0 target 0 a_len;
+  String.unsafe_blit b 0 target a_len b_len;
+  String.unsafe_blit c 0 target (a_len + b_len) c_len;
+  String.unsafe_blit d 0 target (a_len + b_len + c_len) d_len;
+  String.unsafe_blit e 0 target (a_len + b_len + c_len + d_len) e_len;
+  Bytes.unsafe_to_string target
+
+let inter2 a b = concat3 a single_space b
+
+let inter3 a b c = concat5 a single_space b single_space c
+
+let inter4 a b c d = concat_array single_space [|a; b; c; d|]
+
+let parent_dir_lit = ".."
+let current_dir_lit = "."
+
+(* reference {!Bytes.unppercase} *)
+let capitalize_ascii (s : string) : string =
+  if String.length s = 0 then s
+  else
+    let c = String.unsafe_get s 0 in
+    if
+      (c >= 'a' && c <= 'z')
+      || (c >= '\224' && c <= '\246')
+      || (c >= '\248' && c <= '\254')
+    then (
+      let uc = Char.unsafe_chr (Char.code c - 32) in
+      let bytes = Bytes.of_string s in
+      Bytes.unsafe_set bytes 0 uc;
+      Bytes.unsafe_to_string bytes)
+    else s
+
+let capitalize_sub (s : string) len : string =
+  let slen = String.length s in
+  if len < 0 || len > slen then invalid_arg "Ext_string.capitalize_sub"
+  else if len = 0 then ""
+  else
+    let bytes = Bytes.create len in
+    let uc =
+      let c = String.unsafe_get s 0 in
+      if
+        (c >= 'a' && c <= 'z')
+        || (c >= '\224' && c <= '\246')
+        || (c >= '\248' && c <= '\254')
+      then Char.unsafe_chr (Char.code c - 32)
+      else c
+    in
+    Bytes.unsafe_set bytes 0 uc;
+    for i = 1 to len - 1 do
+      Bytes.unsafe_set bytes i (String.unsafe_get s i)
+    done;
+    Bytes.unsafe_to_string bytes
+
+let uncapitalize_ascii = String.uncapitalize_ascii
+
+let lowercase_ascii = String.lowercase_ascii
+
+external ( .![] ) : string -> int -> int = "%string_unsafe_get"
+
+let get_int_1_unsafe (x : string) off : int = x.![off]
+
+let get_int_2_unsafe (x : string) off : int = x.![off] lor (x.![off + 1] lsl 8)
+
+let get_int_3_unsafe (x : string) off : int =
+  x.![off] lor (x.![off + 1] lsl 8) lor (x.![off + 2] lsl 16)
+
+let get_int_4_unsafe (x : string) off : int =
+  x.![off]
+  lor (x.![off + 1] lsl 8)
+  lor (x.![off + 2] lsl 16)
+  lor (x.![off + 3] lsl 24)
+
+let get_1_2_3_4 (x : string) ~off len : int =
+  if len = 1 then get_int_1_unsafe x off
+  else if len = 2 then get_int_2_unsafe x off
+  else if len = 3 then get_int_3_unsafe x off
+  else if len = 4 then get_int_4_unsafe x off
+  else assert false
+
+let unsafe_sub x offs len =
+  let b = Bytes.create len in
+  Ext_bytes.unsafe_blit_string x offs b 0 len;
+  Bytes.unsafe_to_string b
+
+let is_valid_hash_number (x : string) =
+  let len = String.length x in
+  len > 0
+  &&
+  let a = x.![0] in
+  a <= 57
+  &&
+  if len > 1 then
+    a > 48
+    && for_all_from x 1 (function
+         | '0' .. '9' -> true
+         | _ -> false)
+  else a >= 48
+
+let hash_number_as_i32_exn (x : string) : int32 = Int32.of_string x
+
+let first_marshal_char (x : string) = x <> "" && String.unsafe_get x 0 = '\132'
diff --git a/compiler/ext/ext_string.cppo.mli b/compiler/ext/ext_string.mli
similarity index 71%
rename from compiler/ext/ext_string.cppo.mli
rename to compiler/ext/ext_string.mli
index 7099464a239..20fdf3e49b6 100644
--- a/compiler/ext/ext_string.cppo.mli
+++ b/compiler/ext/ext_string.mli
@@ -22,42 +22,32 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)
 
-
-
-
-
-
-
-
 (** Extension to the standard library [String] module, fixed some bugs like
-    avoiding locale sensitivity *) 
+    avoiding locale sensitivity *)
 
-(** default is false *)    
 val split_by : ?keep_empty:bool -> (char -> bool) -> string -> string list
+(** default is false *)
 
-
+val trim : string -> string
 (** remove whitespace letters ('\t', '\n', ' ') on both side*)
-val trim : string -> string 
 
-
-(** default is false *)
 val split : ?keep_empty:bool -> string -> char -> string list
+(** default is false *)
 
+val quick_split_by_ws : string -> string list
 (** split by space chars for quick scripting *)
-val quick_split_by_ws : string -> string list 
-
-
 
 val starts_with : string -> string -> bool
 
+val ends_with_index : string -> string -> int
 (**
    return [-1] when not found, the returned index is useful 
    see [ends_with_then_chop]
 *)
-val ends_with_index : string -> string -> int
 
 val ends_with : string -> string -> bool
 
+val ends_with_then_chop : string -> string -> string option
 (**
    [ends_with_then_chop name ext]
    @example:
@@ -67,30 +57,19 @@ val ends_with : string -> string -> bool
    ]}
    This is useful in controlled or file case sensitve system
 *)
-val ends_with_then_chop : string -> string -> string option
-
-
-
 
+val for_all_from : string -> int -> (char -> bool) -> bool
 (**
    [for_all_from  s start p]
    if [start] is negative, it raises,
    if [start] is too large, it returns true
 *)
-val for_all_from:
-  string -> 
-  int -> 
-  (char -> bool) -> 
-  bool 
 
-val for_all : 
-  string -> 
-  (char -> bool) -> 
-  bool
+val for_all : string -> (char -> bool) -> bool
 
 val is_empty : string -> bool
 
-val repeat : int -> string -> string 
+val repeat : int -> string -> string
 
 val equal : string -> string -> bool
 
@@ -108,12 +87,7 @@ val equal : string -> string -> bool
    char -> 
    string *)
 
-val index_count:  
-  string -> 
-  int ->
-  char -> 
-  int -> 
-  int 
+val index_count : string -> int -> char -> int -> int
 
 (* val index_next :
    string -> 
@@ -121,79 +95,68 @@ val index_count:
    char -> 
    int  *)
 
-
+val find : ?start:int -> sub:string -> string -> int
 (**
    [find ~start ~sub s]
    returns [-1] if not found
 *)
-val find : ?start:int -> sub:string -> string -> int
 
-val contain_substring : string -> string -> bool 
+val contain_substring : string -> string -> bool
 
-val non_overlap_count : sub:string -> string -> int 
+val non_overlap_count : sub:string -> string -> int
 
 val rfind : sub:string -> string -> int
 
+val tail_from : string -> int -> string
 (** [tail_from s 1]
     return a substring from offset 1 (inclusive)
 *)
-val tail_from : string -> int -> string
-
 
+val rindex_neg : string -> char -> int
 (** returns negative number if not found *)
-val rindex_neg : string -> char -> int 
 
 val rindex_opt : string -> char -> int option
 
+val no_char : string -> char -> int -> int -> bool
 
-val no_char : string -> char -> int -> int -> bool 
-
-
-val no_slash : string -> bool 
+val no_slash : string -> bool
 
+val no_slash_idx : string -> int
 (** return negative means no slash, otherwise [i] means the place for first slash *)
-val no_slash_idx : string -> int 
 
-val no_slash_idx_from : string -> int -> int 
+val no_slash_idx_from : string -> int -> int
 
+val replace_slash_backward : string -> string
 (** if no conversion happens, reference equality holds *)
-val replace_slash_backward : string -> string 
 
+val replace_backward_slash : string -> string
 (** if no conversion happens, reference equality holds *)
-val replace_backward_slash : string -> string 
 
-val empty : string 
+val empty : string
 
-#ifdef BROWSER 
-val compare :  string -> string -> int
-#else
-external compare : string -> string -> int = "caml_string_length_based_compare" [@@noalloc];;  
-#endif  
+val compare : string -> string -> int
 val single_space : string
 
-val concat3 : string -> string -> string -> string 
-val concat4 : string -> string -> string -> string -> string 
-val concat5 : string -> string -> string -> string -> string -> string  
+val concat3 : string -> string -> string -> string
+val concat4 : string -> string -> string -> string -> string
+val concat5 : string -> string -> string -> string -> string -> string
 val inter2 : string -> string -> string
-val inter3 : string -> string -> string -> string 
+val inter3 : string -> string -> string -> string
 val inter4 : string -> string -> string -> string -> string
-val concat_array : string -> string array -> string 
+val concat_array : string -> string array -> string
 
-val single_colon : string 
+val single_colon : string
 
 val parent_dir_lit : string
 val current_dir_lit : string
 
 val capitalize_ascii : string -> string
 
-val capitalize_sub:
-  string -> 
-  int -> 
-  string
+val capitalize_sub : string -> int -> string
 
 val uncapitalize_ascii : string -> string
 
-val lowercase_ascii : string -> string 
+val lowercase_ascii : string -> string
 
 (** Play parity to {!Ext_buffer.add_int_1} *)
 (* val get_int_1 : string -> int -> int 
@@ -201,26 +164,12 @@ val lowercase_ascii : string -> string
    val get_int_3 : string -> int -> int 
    val get_int_4 : string -> int -> int  *)
 
-val get_1_2_3_4 : 
-  string -> 
-  off:int ->  
-  int -> 
-  int 
-
-val unsafe_sub :   
-  string -> 
-  int -> 
-  int -> 
-  string
-
-val is_valid_hash_number:
-  string -> 
-  bool
-
-val hash_number_as_i32_exn:
-  string ->
-  int32
-
-val first_marshal_char:  
-  string -> 
-  bool
+val get_1_2_3_4 : string -> off:int -> int -> int
+
+val unsafe_sub : string -> int -> int -> string
+
+val is_valid_hash_number : string -> bool
+
+val hash_number_as_i32_exn : string -> int32
+
+val first_marshal_char : string -> bool
diff --git a/compiler/ext/ext_sys.cppo.ml b/compiler/ext/ext_sys.ml
similarity index 85%
rename from compiler/ext/ext_sys.cppo.ml
rename to compiler/ext/ext_sys.ml
index 917d397550e..c5412249222 100644
--- a/compiler/ext/ext_sys.cppo.ml
+++ b/compiler/ext/ext_sys.ml
@@ -22,15 +22,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)
 
-(** TODO: not exported yet, wait for Windows Fix*)
-#ifdef BROWSER
-let is_directory_no_exn f =
-  try Sys.is_directory f with _ -> false  
-#else
-external is_directory_no_exn : string -> bool = "caml_sys_is_directory_no_exn"
-#endif
-
+(* Sys.is_directory is available on every supported compiler target. *)
+let is_directory_no_exn file = try Sys.is_directory file with _ -> false
 
 let is_windows_or_cygwin = Sys.win32 || Sys.cygwin
-
-
diff --git a/compiler/ext/hash.cppo.ml b/compiler/ext/hash.cppo.ml
index 6194e414ea8..905d1c97ea2 100644
--- a/compiler/ext/hash.cppo.ml
+++ b/compiler/ext/hash.cppo.ml
@@ -2,20 +2,19 @@
 type key = Ident.t 
 type 'a t = (key, 'a)  Hash_gen.t 
 let key_index (h : _ t ) (key : key) =
-  (Bs_hash_stubs.hash_stamp_and_name  key.stamp key.name ) land (Array.length h.data - 1)
-(* (Bs_hash_stubs.hash_string_int  key.name key.stamp ) land (Array.length h.data - 1) *)
+  (Ext_platform_primitives.hash_stamp_and_name  key.stamp key.name ) land (Array.length h.data - 1)
 let eq_key = Ext_ident.equal 
 #elif defined TYPE_STRING
 type key = string
 type 'a t = (key, 'a)  Hash_gen.t 
 let key_index (h : _ t ) (key : key) =
-  (Bs_hash_stubs.hash_string  key ) land (Array.length h.data - 1)
+  (Ext_platform_primitives.hash_string  key ) land (Array.length h.data - 1)
 let eq_key = Ext_string.equal 
 #elif defined TYPE_INT
 type key = int 
 type 'a t = (key, 'a)  Hash_gen.t 
 let key_index (h : _ t ) (key : key) =
-  (Bs_hash_stubs.hash_int  key ) land (Array.length h.data - 1)
+  (Ext_platform_primitives.hash_int  key ) land (Array.length h.data - 1)
 let eq_key = Ext_int.equal   
 
 #elif defined TYPE_FUNCTOR
diff --git a/compiler/ext/hash_set.cppo.ml b/compiler/ext/hash_set.cppo.ml
index 73779079ad2..93b51a340c4 100644
--- a/compiler/ext/hash_set.cppo.ml
+++ b/compiler/ext/hash_set.cppo.ml
@@ -25,19 +25,19 @@
 #ifdef TYPE_INT
 type key = int
 let key_index (h :  _ Hash_set_gen.t ) (key : key) =
-  (Bs_hash_stubs.hash_int  key) land (Array.length h.data - 1)
+  (Ext_platform_primitives.hash_int  key) land (Array.length h.data - 1)
 let eq_key = Ext_int.equal 
 type  t = key  Hash_set_gen.t 
 #elif defined TYPE_STRING
 type key = string 
 let key_index (h :  _ Hash_set_gen.t ) (key : key) =
-  (Bs_hash_stubs.hash_string  key) land (Array.length h.data - 1)
+  (Ext_platform_primitives.hash_string  key) land (Array.length h.data - 1)
 let eq_key = Ext_string.equal 
 type  t = key  Hash_set_gen.t 
 #elif defined TYPE_IDENT
 type key = Ident.t
 let key_index (h :  _ Hash_set_gen.t ) (key : key) =
-  (Bs_hash_stubs.hash_string_int  key.name key.stamp) land (Array.length h.data - 1)
+  (Ext_platform_primitives.hash_string_int  key.name key.stamp) land (Array.length h.data - 1)
 let eq_key = Ext_ident.equal
 type t = key Hash_set_gen.t
 #elif defined TYPE_FUNCTOR
@@ -121,4 +121,3 @@ module Make (H: Hashtbl.HashedType) : (Hash_set_gen.S with type key = H.t) = str
 #ifdef TYPE_FUNCTOR
 end
 #endif
-
diff --git a/compiler/ext/hash_set_ident_mask.ml b/compiler/ext/hash_set_ident_mask.ml
index 67a78d836d8..2d7722f1305 100644
--- a/compiler/ext/hash_set_ident_mask.ml
+++ b/compiler/ext/hash_set_ident_mask.ml
@@ -35,7 +35,8 @@ type t = {
 }
 
 let key_index_by_ident (h : t) (key : Ident.t) =
-  Bs_hash_stubs.hash_string_int key.name key.stamp land (Array.length h.data - 1)
+  Ext_platform_primitives.hash_string_int key.name key.stamp
+  land (Array.length h.data - 1)
 
 let create initial_size =
   let s = Ext_util.power_2_above 8 initial_size in
diff --git a/compiler/ext/js_reserved_map.cppo.ml b/compiler/ext/js_reserved_map.ml
similarity index 52%
rename from compiler/ext/js_reserved_map.cppo.ml
rename to compiler/ext/js_reserved_map.ml
index 6daaff97601..9950bf89ca1 100644
--- a/compiler/ext/js_reserved_map.cppo.ml
+++ b/compiler/ext/js_reserved_map.ml
@@ -23,16 +23,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)
 
 module STbl = struct
-  #if OCAML_VERSION >= (5, 0, 0)
-    include Hashtbl.Make (String)
-  #else
-    module StringHash : Hashtbl.HashedType with type t = string = struct
-      type t = string
-      let equal = String.equal
-      let hash = Hashtbl.hash (* polymorphic hash function *)
-    end
-    include Hashtbl.Make (StringHash)
-  #endif
+  include Hashtbl.Make (String)
 
   let of_array arr =
     let tbl = create (Array.length arr) in
@@ -44,61 +35,59 @@ end
 
     See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#reserved_words
  *)
-let js_keywords = STbl.of_array [|
-  "break";
-  "case";
-  "catch";
-  "class";
-  "const";
-  "continue";
-  "debugger";
-  "default";
-  "delete";
-  "do";
-  "else";
-  "export";
-  "extends";
-  "false";
-  "finally";
-  "for";
-  "function";
-  "if";
-  "import";
-  "in";
-  "instanceof";
-  "new";
-  "null";
-  "return";
-  "super";
-  "switch";
-  "this";
-  "throw";
-  "true";
-  "try";
-  "typeof";
-  "var";
-  "void";
-  "while";
-  "with";
-
-  (* The following are also reserved in strict context, including ESM *)
-  "let";
-  "static";
-  "yield";
-
-  (* `await` is reserved in async context, including ESM *)
-  "await";
-
-  (* Future reserved words *)
-  "enum";
-  "implements";
-  "interface";
-  "package";
-  "private";
-  "protected";
-  "public";
-
-  (* Special identifiers
+let js_keywords =
+  STbl.of_array
+    [|
+      "break";
+      "case";
+      "catch";
+      "class";
+      "const";
+      "continue";
+      "debugger";
+      "default";
+      "delete";
+      "do";
+      "else";
+      "export";
+      "extends";
+      "false";
+      "finally";
+      "for";
+      "function";
+      "if";
+      "import";
+      "in";
+      "instanceof";
+      "new";
+      "null";
+      "return";
+      "super";
+      "switch";
+      "this";
+      "throw";
+      "true";
+      "try";
+      "typeof";
+      "var";
+      "void";
+      "while";
+      "with";
+      (* The following are also reserved in strict context, including ESM *)
+      "let";
+      "static";
+      "yield";
+      (* `await` is reserved in async context, including ESM *)
+      "await";
+      (* Future reserved words *)
+      "enum";
+      "implements";
+      "interface";
+      "package";
+      "private";
+      "protected";
+      "public";
+      (* Special identifiers
 
      `arguments` and `eval` is not real *keywords*
 
@@ -107,9 +96,9 @@ let js_keywords = STbl.of_array [|
 
      See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#identifiers_with_special_meanings
    *)
-  "arguments";
-  "eval";
-|]
+      "arguments";
+      "eval";
+    |]
 
 let is_js_keyword s = STbl.mem js_keywords s
 
@@ -121,93 +110,87 @@ let is_js_keyword s = STbl.mem js_keywords s
 
     However, these names are actually used with no problems today. (Except `arguments` and `eval`)
  *)
-let js_special_words = STbl.of_array [|
-  "arguments";
-  "as";
-  "async";
-  "eval";
-  "from";
-  "get";
-  "of";
-  "set";
-|]
+let js_special_words =
+  STbl.of_array
+    [|"arguments"; "as"; "async"; "eval"; "from"; "get"; "of"; "set"|]
 
 let is_js_special_word s = STbl.mem js_special_words s
 
 (** Identifier names _might_ need to care about *)
-let js_globals = STbl.of_array [|
-  (* JavaScript standards built-ins
+let js_globals =
+  STbl.of_array
+    [|
+      (* JavaScript standards built-ins
      See https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Global_Objects
   *)
-  "AggregateError";
-  "Array";
-  "ArrayBuffer";
-  "AsyncFunction";
-  "AsyncGenerator";
-  "AsyncGeneratorFunction";
-  "AsyncIterator";
-  "Atomics";
-  "BigInt";
-  "BigInt64Array";
-  "BigUint64Array";
-  "Boolean";
-  "DataView";
-  "Date";
-  "decodeURI";
-  "decodeURIComponent";
-  "encodeURI";
-  "encodeURIComponent";
-  "Error";
-  "eval";
-  "EvalError";
-  "FinalizationRegistry";
-  "Float16Array";
-  "Float32Array";
-  "Float64Array";
-  "Function";
-  "Generator";
-  "GeneratorFunction";
-  "globalThis";
-  "Infinity";
-  "Int16Array";
-  "Int32Array";
-  "Int8Array";
-  "Intl";
-  "isFinite";
-  "isNaN";
-  "Iterator";
-  "JSON";
-  "Map";
-  "Math";
-  "NaN";
-  "Number";
-  "Object";
-  "parseFloat";
-  "parseInt";
-  "Promise";
-  "Proxy";
-  "RangeError";
-  "ReferenceError";
-  "Reflect";
-  "RegExp";
-  "Set";
-  "SharedArrayBuffer";
-  "String";
-  "Symbol";
-  "SyntaxError";
-  "TypedArray";
-  "TypeError";
-  "Uint16Array";
-  "Uint32Array";
-  "Uint8Array";
-  "Uint8ClampedArray";
-  "undefined";
-  "URIError";
-  "WeakMap";
-  "WeakRef";
-  "WeakSet";
-
-  (* A few of the HTML standard globals
+      "AggregateError";
+      "Array";
+      "ArrayBuffer";
+      "AsyncFunction";
+      "AsyncGenerator";
+      "AsyncGeneratorFunction";
+      "AsyncIterator";
+      "Atomics";
+      "BigInt";
+      "BigInt64Array";
+      "BigUint64Array";
+      "Boolean";
+      "DataView";
+      "Date";
+      "decodeURI";
+      "decodeURIComponent";
+      "encodeURI";
+      "encodeURIComponent";
+      "Error";
+      "eval";
+      "EvalError";
+      "FinalizationRegistry";
+      "Float16Array";
+      "Float32Array";
+      "Float64Array";
+      "Function";
+      "Generator";
+      "GeneratorFunction";
+      "globalThis";
+      "Infinity";
+      "Int16Array";
+      "Int32Array";
+      "Int8Array";
+      "Intl";
+      "isFinite";
+      "isNaN";
+      "Iterator";
+      "JSON";
+      "Map";
+      "Math";
+      "NaN";
+      "Number";
+      "Object";
+      "parseFloat";
+      "parseInt";
+      "Promise";
+      "Proxy";
+      "RangeError";
+      "ReferenceError";
+      "Reflect";
+      "RegExp";
+      "Set";
+      "SharedArrayBuffer";
+      "String";
+      "Symbol";
+      "SyntaxError";
+      "TypedArray";
+      "TypeError";
+      "Uint16Array";
+      "Uint32Array";
+      "Uint8Array";
+      "Uint8ClampedArray";
+      "undefined";
+      "URIError";
+      "WeakMap";
+      "WeakRef";
+      "WeakSet";
+      (* A few of the HTML standard globals
   
      See https://developer.mozilla.org/en-US/docs/Web/API/Window
      See https://developer.mozilla.org/en-US/docs/Web/API/WorkerGlobalScope
@@ -222,22 +205,20 @@ let js_globals = STbl.of_array [|
   "origin";
   *)
 
-  (* A few of the Node.js globals
+      (* A few of the Node.js globals
   
      Specifically related to the CommonJS module system
      They cannot be redeclared in nested scope.
   *)
-  "__dirname";
-  "__filename";
-  "require";
-  "module";
-  "exports";
-
-  (* Bun's global namespace *)
-  "Bun";
-
-  (* Deno's global namespace *)
-  "Deno";
-|]
+      "__dirname";
+      "__filename";
+      "require";
+      "module";
+      "exports";
+      (* Bun's global namespace *)
+      "Bun";
+      (* Deno's global namespace *)
+      "Deno";
+    |]
 
 let is_js_global s = STbl.mem js_globals s
diff --git a/compiler/ext/ordered_hash_map.cppo.ml b/compiler/ext/ordered_hash_map.cppo.ml
index b44ef6679e9..24ec39b2797 100644
--- a/compiler/ext/ordered_hash_map.cppo.ml
+++ b/compiler/ext/ordered_hash_map.cppo.ml
@@ -10,7 +10,7 @@ struct
   type key = Ident.t
   type   'value t = (key,'value) Ordered_hash_map_gen.t
   let key_index (h : _ t) (key : key) =
-    (Bs_hash_stubs.hash_int  key.stamp) land (Array.length h.data - 1)
+    (Ext_platform_primitives.hash_int  key.stamp) land (Array.length h.data - 1)
   let equal_key = Ext_ident.equal
 
 #else
@@ -108,4 +108,3 @@ end
 
 
 
-
diff --git a/compiler/ext/platform/native/ext_platform_primitives.ml b/compiler/ext/platform/native/ext_platform_primitives.ml
new file mode 100644
index 00000000000..96d4c23bb8b
--- /dev/null
+++ b/compiler/ext/platform/native/ext_platform_primitives.ml
@@ -0,0 +1,19 @@
+(* Native optimized compiler primitives. *)
+external hash_string : string -> int = "caml_bs_hash_string" [@@noalloc]
+
+external hash_string_int : string -> int -> int = "caml_bs_hash_string_and_int"
+[@@noalloc]
+
+external hash_stamp_and_name : int -> string -> int
+  = "caml_bs_hash_stamp_and_name"
+[@@noalloc]
+
+external hash_int : int -> int = "caml_bs_hash_int" [@@noalloc]
+
+external string_length_based_compare : string -> string -> int
+  = "caml_string_length_based_compare"
+[@@noalloc]
+
+external int_unsafe_blit : int array -> int -> int array -> int -> int -> unit
+  = "caml_int_array_blit"
+[@@noalloc]
diff --git a/compiler/ext/platform/playground/ext_platform_primitives.ml b/compiler/ext/platform/playground/ext_platform_primitives.ml
new file mode 100644
index 00000000000..4eaea3dd3b4
--- /dev/null
+++ b/compiler/ext/platform/playground/ext_platform_primitives.ml
@@ -0,0 +1,13 @@
+(* Portable compiler primitives used by the playground. *)
+let hash_string : string -> int = Hashtbl.hash
+let hash_string_int string int = Hashtbl.hash (string, int)
+let hash_stamp_and_name int string = Hashtbl.hash (int, string)
+let hash_int : int -> int = Hashtbl.hash
+
+let string_length_based_compare x y =
+  let x_length = String.length x in
+  let y_length = String.length y in
+  if x_length = y_length then String.compare x y
+  else Int.compare x_length y_length
+
+let int_unsafe_blit = Array.blit
diff --git a/compiler/ext/vec.cppo.ml b/compiler/ext/vec.cppo.ml
index 6e8ba607f02..14027008aa0 100644
--- a/compiler/ext/vec.cppo.ml
+++ b/compiler/ext/vec.cppo.ml
@@ -37,7 +37,7 @@ module Make ( Resize :  Vec_gen.ResizeType) = struct
 
 type elt = int 
 let null = 0 (* can be optimized *)
-let unsafe_blit = Bs_hash_stubs.int_unsafe_blit
+let unsafe_blit = Ext_platform_primitives.int_unsafe_blit
 #else 
 [%error "unknown type"]
 #endif
diff --git a/compiler/ml/cmt_format.ml b/compiler/ml/cmt_format.ml
new file mode 100644
index 00000000000..d96c006ac00
--- /dev/null
+++ b/compiler/ml/cmt_format.ml
@@ -0,0 +1,6 @@
+include Cmt_format_common
+
+let save_cmt filename modname binary_annots sourcefile initial_env cmi =
+  Cmt_format_persistence.save_cmt filename modname binary_annots sourcefile
+    initial_env cmi;
+  clear ()
diff --git a/compiler/ml/cmt_format.mli b/compiler/ml/cmt_format.mli
index 66589f088de..9d37721f1b8 100644
--- a/compiler/ml/cmt_format.mli
+++ b/compiler/ml/cmt_format.mli
@@ -58,7 +58,7 @@ type cmt_infos = {
   cmt_sourcefile: string option;
   cmt_builddir: string;
   cmt_loadpath: string list;
-  cmt_source_digest: string option;
+  cmt_source_digest: Digest.t option;
   cmt_initial_env: Env.t;
   cmt_imports: (string * Digest.t option) list;
   cmt_interface_digest: Digest.t option;
diff --git a/compiler/ml/cmt_format.cppo.ml b/compiler/ml/cmt_format_common.ml
similarity index 52%
rename from compiler/ml/cmt_format.cppo.ml
rename to compiler/ml/cmt_format_common.ml
index ff30fc00435..d3a151f9444 100644
--- a/compiler/ml/cmt_format.cppo.ml
+++ b/compiler/ml/cmt_format_common.ml
@@ -13,24 +13,12 @@
 (*                                                                        *)
 (**************************************************************************)
 
-#ifdef BROWSER
-[@@@warning "-32"]
-#endif
+(* Shared CMT reading and collection logic. Persistence is supplied by the
+   selected Cmt_format implementation so the playground does not retain the
+   native writer and its transitive dependencies. *)
 
 open Typedtree
 
-(* Note that in Typerex, there is an awful hack to save a cmt file
-   together with the interface file that was generated by ocaml (this
-   is because the installed version of ocaml might differ from the one
-   integrated in Typerex).
-*)
-
-
-
-let read_magic_number ic =
-  let len_magic_number = String.length Config.cmt_magic_number in
-  really_input_string ic len_magic_number
-
 type binary_annots =
   | Packed of Types.signature * string list
   | Implementation of structure
@@ -39,38 +27,49 @@ type binary_annots =
   | Partial_interface of binary_part array
 
 and binary_part =
-| Partial_structure of structure
-| Partial_structure_item of structure_item
-| Partial_expression of expression
-| Partial_pattern of pattern
-| Partial_class_expr of unit
-| Partial_signature of signature
-| Partial_signature_item of signature_item
-| Partial_module_type of module_type
+  | Partial_structure of structure
+  | Partial_structure_item of structure_item
+  | Partial_expression of expression
+  | Partial_pattern of pattern
+  | Partial_class_expr of unit
+  | Partial_signature of signature
+  | Partial_signature_item of signature_item
+  | Partial_module_type of module_type
 
 type cmt_infos = {
-  cmt_modname : string;
-  cmt_annots : binary_annots;
-  cmt_value_dependencies :
+  cmt_modname: string;
+  cmt_annots: binary_annots;
+  cmt_value_dependencies:
     (Types.value_description * Types.value_description) list;
-  cmt_comments : (string * Location.t) list;
-  cmt_args : string array;
-  cmt_sourcefile : string option;
-  cmt_builddir : string;
-  cmt_loadpath : string list;
-  cmt_source_digest : Digest.t option;
-  cmt_initial_env : Env.t;
-  cmt_imports : (string * Digest.t option) list;
-  cmt_interface_digest : Digest.t option;
-  cmt_use_summaries : bool;
+  cmt_comments: (string * Location.t) list;
+  cmt_args: string array;
+  cmt_sourcefile: string option;
+  cmt_builddir: string;
+  cmt_loadpath: string list;
+  cmt_source_digest: Digest.t option;
+  cmt_initial_env: Env.t;
+  cmt_imports: (string * Digest.t option) list;
+  cmt_interface_digest: Digest.t option;
+  cmt_use_summaries: bool;
   cmt_extra_info: Cmt_utils.cmt_extra_info;
 }
 
-type error =
-    Not_a_typedtree of string
+(* Note that in Typerex, there is an awful hack to save a cmt file
+   together with the interface file that was generated by ocaml (this
+   is because the installed version of ocaml might differ from the one
+   integrated in Typerex).
+*)
+
+let read_magic_number ic =
+  let len_magic_number = String.length Config.cmt_magic_number in
+  really_input_string ic len_magic_number
+
+type error = Not_a_typedtree of string
 
 let need_to_clear_env =
-  try ignore (Sys.getenv "OCAML_BINANNOT_WITHENV"); false
+  try
+    ignore (Sys.getenv "OCAML_BINANNOT_WITHENV");
+    false
   with Not_found -> true
 
 let keep_only_summary = Env.keep_only_summary
@@ -78,18 +77,18 @@ let keep_only_summary = Env.keep_only_summary
 open Tast_mapper
 
 let cenv =
-  {Tast_mapper.default with env = fun _sub env -> keep_only_summary env}
+  {Tast_mapper.default with env = (fun _sub env -> keep_only_summary env)}
 
 let clear_part = function
   | Partial_structure s -> Partial_structure (cenv.structure cenv s)
   | Partial_structure_item s ->
-      Partial_structure_item (cenv.structure_item cenv s)
+    Partial_structure_item (cenv.structure_item cenv s)
   | Partial_expression e -> Partial_expression (cenv.expr cenv e)
   | Partial_pattern p -> Partial_pattern (cenv.pat cenv p)
   | Partial_class_expr () -> assert false
   | Partial_signature s -> Partial_signature (cenv.signature cenv s)
   | Partial_signature_item s ->
-      Partial_signature_item (cenv.signature_item cenv s)
+    Partial_signature_item (cenv.signature_item cenv s)
   | Partial_module_type s -> Partial_module_type (cenv.module_type cenv s)
 
 let clear_env binary_annots =
@@ -99,63 +98,61 @@ let clear_env binary_annots =
     | Interface s -> Interface (cenv.signature cenv s)
     | Packed _ -> binary_annots
     | Partial_implementation array ->
-        Partial_implementation (Array.map clear_part array)
-    | Partial_interface array ->
-        Partial_interface (Array.map clear_part array)
-
+      Partial_implementation (Array.map clear_part array)
+    | Partial_interface array -> Partial_interface (Array.map clear_part array)
   else binary_annots
 
 exception Error of error
 
 let input_cmt ic = (input_value ic : cmt_infos)
 
-let output_cmt oc cmt =
-  output_string oc Config.cmt_magic_number;
-  output_value oc (cmt : cmt_infos)
-
 let read filename =
-(*  Printf.fprintf stderr "Cmt_format.read %s\n%!" filename; *)
+  (*  Printf.fprintf stderr "Cmt_format.read %s\n%!" filename; *)
   let ic = open_in_bin filename in
   try
     let magic_number = read_magic_number ic in
     let cmi, cmt =
-      if magic_number = Config.cmt_magic_number then
-        None, Some (input_cmt ic)
+      if magic_number = Config.cmt_magic_number then (None, Some (input_cmt ic))
       else if magic_number = Config.cmi_magic_number then
         let cmi = Cmi_format.input_cmi ic in
-        let cmt = try
-                    let magic_number = read_magic_number ic in
-                    if magic_number = Config.cmt_magic_number then
-                      let cmt = input_cmt ic in
-                      Some cmt
-                    else None
+        let cmt =
+          try
+            let magic_number = read_magic_number ic in
+            if magic_number = Config.cmt_magic_number then
+              let cmt = input_cmt ic in
+              Some cmt
+            else None
           with _ -> None
         in
-        Some cmi, cmt
-      else
-        raise(Cmi_format.Error(Cmi_format.Not_an_interface filename))
+        (Some cmi, cmt)
+      else raise (Cmi_format.Error (Cmi_format.Not_an_interface filename))
     in
     close_in ic;
-(*    Printf.fprintf stderr "Cmt_format.read done\n%!"; *)
-    cmi, cmt
+    (*    Printf.fprintf stderr "Cmt_format.read done\n%!"; *)
+    (cmi, cmt)
   with e ->
     close_in ic;
     raise e
 
 let read_cmt filename =
   match read filename with
-      _, None -> raise (Error (Not_a_typedtree filename))
-    | _, Some cmt -> cmt
+  | _, None -> raise (Error (Not_a_typedtree filename))
+  | _, Some cmt -> cmt
 
 let read_cmi filename =
   match read filename with
-      None, _ ->
-        raise (Cmi_format.Error (Cmi_format.Not_an_interface filename))
-    | Some cmi, _ -> cmi
+  | None, _ -> raise (Cmi_format.Error (Cmi_format.Not_an_interface filename))
+  | Some cmi, _ -> cmi
+
+let saved_types : binary_part list ref = ref []
 
-let saved_types = ref []
-let value_deps = ref []
-let deprecated_used = ref []
+let value_deps : (Types.value_description * Types.value_description) list ref =
+  ref []
+
+let deprecated_used : Cmt_utils.deprecated_used list ref = ref []
+
+let value_dependencies () = !value_deps
+let deprecated_uses () = !deprecated_used
 
 let clear () =
   saved_types := [];
@@ -166,7 +163,8 @@ let add_saved_type b = saved_types := b :: !saved_types
 let get_saved_types () = !saved_types
 let set_saved_types l = saved_types := l
 
-let record_deprecated_used ?deprecated_context ?migration_template ?migration_in_pipe_chain_template source_loc deprecated_text =
+let record_deprecated_used ?deprecated_context ?migration_template
+    ?migration_in_pipe_chain_template source_loc deprecated_text =
   deprecated_used :=
     {
       Cmt_utils.source_loc;
@@ -182,40 +180,3 @@ let _ = Cmt_utils.record_deprecated_used := record_deprecated_used
 let record_value_dependency vd1 vd2 =
   if vd1.Types.val_loc <> vd2.Types.val_loc then
     value_deps := (vd1, vd2) :: !value_deps
-
-#ifdef BROWSER
-let save_cmt _filename _modname _binary_annots _sourcefile _initial_env _cmi = ()  
-#else
-open Cmi_format
-
-let save_cmt filename modname binary_annots sourcefile initial_env cmi =
-  if !Clflags.binary_annotations then begin
-    Misc.output_to_bin_file_directly filename
-       (fun temp_file_name oc ->
-         let this_crc =
-           match cmi with
-           | None -> None
-           | Some cmi -> Some (output_cmi temp_file_name oc cmi)
-         in
-         let source_digest = Misc.may_map Digest.file sourcefile in
-         let cmt = {
-           cmt_modname = modname;
-           cmt_annots = clear_env binary_annots;
-           cmt_value_dependencies = !value_deps;
-           cmt_comments = [];
-           cmt_args = Sys.argv;
-           cmt_sourcefile = sourcefile;
-           cmt_builddir =  Sys.getcwd ();
-           cmt_loadpath = !Config.load_path;
-           cmt_source_digest = source_digest;
-           cmt_initial_env = if need_to_clear_env then
-               keep_only_summary initial_env else initial_env;
-           cmt_imports = List.sort compare (Env.imports ());
-           cmt_interface_digest = this_crc;
-           cmt_use_summaries = need_to_clear_env;
-           cmt_extra_info = {deprecated_used = !deprecated_used};
-         } in
-         output_cmt oc cmt)
-  end;
-  clear ()
-#endif
diff --git a/compiler/ml/dune b/compiler/ml/dune
index a5a53b70c3f..7a286e14044 100644
--- a/compiler/ml/dune
+++ b/compiler/ml/dune
@@ -1,14 +1,30 @@
+(env
+ (_
+  (flags
+   (:standard -w +a-4-42-40-41-44-45-9-48-67-70))))
+
+; The browser profile builds the playground compiler; this rule pair generates a module from platform/{native,playground}.
+
+(rule
+ (target cmt_format_persistence.ml)
+ (enabled_if
+  (= %{profile} browser))
+ (action
+  (copy
+   platform/playground/cmt_format_persistence.ml
+   cmt_format_persistence.ml)))
+
+(rule
+ (target cmt_format_persistence.ml)
+ (enabled_if
+  (<> %{profile} browser))
+ (action
+  (copy platform/native/cmt_format_persistence.ml cmt_format_persistence.ml)))
+
 (library
  (name ml)
  (wrapped false)
+ (private_modules cmt_format_common cmt_format_persistence)
  (instrumentation
   (backend bisect_ppx))
- (flags
-  (:standard -w +a-4-42-40-41-44-45-9-48-67-70))
  (libraries ext flow_parser))
-
-(rule
- (target cmt_format.ml)
- (deps cmt_format.cppo.ml)
- (action
-  (run %{bin:cppo} %{env:CPPO_FLAGS=} %{deps} -o %{target})))
diff --git a/compiler/ml/platform/native/cmt_format_persistence.ml b/compiler/ml/platform/native/cmt_format_persistence.ml
new file mode 100644
index 00000000000..b98fef30e8c
--- /dev/null
+++ b/compiler/ml/platform/native/cmt_format_persistence.ml
@@ -0,0 +1,52 @@
+(**************************************************************************)
+(*                                                                        *)
+(*                                 OCaml                                  *)
+(*                                                                        *)
+(*                   Fabrice Le Fessant, INRIA Saclay                     *)
+(*                                                                        *)
+(*   Copyright 2012 Institut National de Recherche en Informatique et     *)
+(*     en Automatique.                                                    *)
+(*                                                                        *)
+(*   All rights reserved.  This file is distributed under the terms of    *)
+(*   the GNU Lesser General Public License version 2.1, with the          *)
+(*   special exception on linking described in the file LICENSE.          *)
+(*                                                                        *)
+(**************************************************************************)
+
+open Cmt_format_common
+
+let output_cmt output_channel cmt =
+  output_string output_channel Config.cmt_magic_number;
+  output_value output_channel (cmt : cmt_infos)
+
+let save_cmt filename modname binary_annots sourcefile initial_env cmi =
+  if !Clflags.binary_annotations then
+    Misc.output_to_bin_file_directly filename
+      (fun temp_file_name output_channel ->
+        let interface_digest =
+          match cmi with
+          | None -> None
+          | Some cmi ->
+            Some (Cmi_format.output_cmi temp_file_name output_channel cmi)
+        in
+        let cmt =
+          {
+            cmt_modname = modname;
+            cmt_annots = clear_env binary_annots;
+            cmt_value_dependencies = value_dependencies ();
+            cmt_comments = [];
+            cmt_args = Sys.argv;
+            cmt_sourcefile = sourcefile;
+            cmt_builddir = Sys.getcwd ();
+            cmt_loadpath = !Config.load_path;
+            cmt_source_digest = Misc.may_map Digest.file sourcefile;
+            cmt_initial_env =
+              (if need_to_clear_env then keep_only_summary initial_env
+               else initial_env);
+            cmt_imports = List.sort compare (Env.imports ());
+            cmt_interface_digest = interface_digest;
+            cmt_use_summaries = need_to_clear_env;
+            cmt_extra_info = {deprecated_used = deprecated_uses ()};
+          }
+        in
+        output_cmt output_channel cmt)
diff --git a/compiler/ml/platform/playground/cmt_format_persistence.ml b/compiler/ml/platform/playground/cmt_format_persistence.ml
new file mode 100644
index 00000000000..2fc0fe177c4
--- /dev/null
+++ b/compiler/ml/platform/playground/cmt_format_persistence.ml
@@ -0,0 +1,2 @@
+let save_cmt _filename _modname _binary_annots _sourcefile _initial_env _cmi =
+  ()
diff --git a/tests/ERROR_VARIANTS.md b/tests/ERROR_VARIANTS.md
index afeba3034e4..36595660b69 100644
--- a/tests/ERROR_VARIANTS.md
+++ b/tests/ERROR_VARIANTS.md
@@ -473,7 +473,7 @@ Build / dependency errors. Mostly need the `rescript build` runtime to fire —
 | `Bs_main_not_exist` | ☐ (needs build harness) | — | `rescript.json` `main` entry missing. |
 | `Bs_invalid_path` | ☐ (needs build harness) | — | `-I` / source path with invalid form. |
 | `Missing_ml_dependency` | ☐ (needs build harness) | — | Compile-time missing dependency from a `.cmj` lookup table. |
-| `Dependency_script_module_dependent_not` | ☐ (needs build harness) | — | `js_name_of_module_id.cppo.ml:122`. **Reachable** when a dependent module is in script mode (`Package_script`) but the current module is in package mode (`Package_found _`). Legacy script-vs-package interaction; needs `rescript.json` harness. |
+| `Dependency_script_module_dependent_not` | ☐ (needs build harness) | — | `core/platform/native/js_name_of_module_id.ml:99`. **Reachable** when a dependent module is in script mode (`Package_script`) but the current module is in package mode (`Package_found _`). Legacy script-vs-package interaction; needs `rescript.json` harness. |
 
 ---
 
@@ -529,7 +529,7 @@ multi-file harnesses, which never set `-ppx`.
 | `compiler/ml/transl_recmodule.ml` | `Circular_dependency` | ✓ | `recmodule_circular_dependency.res` | |
 | `compiler/ml/rec_check.ml` | `Illegal_letrec_expr` | ✓ | `illegal_letrec_expr.res` | |
 | `compiler/ml/syntaxerr.ml` | `Variable_in_scope` | ? (live, broken printer) | — | Reachable via `let f: type t. (t, 't) => t = …` (locally-abstract `t` collides with type variable `'t` during `varify_constructors`), but `Syntaxerr.error` has no registered pretty-printer, so it propagates as an uncaught `Fatal error: exception Syntaxerr.Error(_)`. Not removed because the variant is live; the fix should wire up a printer or convert the check into a regular typed diagnostic. |
-| `compiler/ml/cmt_format.cppo.ml` | `Not_a_typedtree` | ☐ (needs binary harness) | — | cmt_format.cppo.ml:147. Fires when a tool reads a `.cmt` file whose first block isn't a typed tree. Reachable in principle by pointing the analyzer at an arbitrary file with a `.cmt` extension; out of scope for the source-only fixture harnesses. |
+| `compiler/ml/cmt_format_common.ml` | `Not_a_typedtree` | ☐ (needs binary harness) | — | cmt_format_common.ml:139. Fires when a tool reads a `.cmt` file whose first block isn't a typed tree. Reachable in principle by pointing the analyzer at an arbitrary file with a `.cmt` extension; out of scope for the source-only fixture harnesses. |
 | `compiler/ext/bsc_args.ml` | `Unknown` | ☐ (needs CLI harness) | — | bsc_args.ml:45. Reachable trivially via `bsc --bogus`, but the `super_errors{,_multi}` runners only pass `bsc` a fixed flag list plus the source file — they can't exercise CLI-level errors. |
 | `compiler/ext/bsc_args.ml` | `Missing` | ☐ (needs CLI harness) | — | Same as above: `bsc -o` (no following filename). Needs a harness that invokes `bsc` with crafted argv. |
 
diff --git a/tests/ounit_tests/ounit_hash_stubs_test.ml b/tests/ounit_tests/ounit_hash_stubs_test.ml
index 6f686653c3e..0c033af7f22 100644
--- a/tests/ounit_tests/ounit_hash_stubs_test.ml
+++ b/tests/ounit_tests/ounit_hash_stubs_test.ml
@@ -27,39 +27,34 @@ let bench () =
       done)
 
 type id = {stamp: int; name: string; mutable flags: int} (* = Ident.t *)
-let hash id = Bs_hash_stubs.hash_stamp_and_name id.stamp id.name
+let hash id = Ext_platform_primitives.hash_stamp_and_name id.stamp id.name
 let suites =
   __FILE__
   >::: [
-         (__LOC__ >:: fun _ -> Bs_hash_stubs.hash_int 0 =~ Hashtbl.hash 0);
          ( __LOC__ >:: fun _ ->
-           Bs_hash_stubs.hash_int max_int =~ Hashtbl.hash max_int );
+           Ext_platform_primitives.hash_int 0 =~ Hashtbl.hash 0 );
          ( __LOC__ >:: fun _ ->
-           Bs_hash_stubs.hash_int max_int =~ Hashtbl.hash max_int );
+           Ext_platform_primitives.hash_int max_int =~ Hashtbl.hash max_int );
          ( __LOC__ >:: fun _ ->
-           Bs_hash_stubs.hash_string
+           Ext_platform_primitives.hash_int max_int =~ Hashtbl.hash max_int );
+         ( __LOC__ >:: fun _ ->
+           Ext_platform_primitives.hash_string
              "The quick brown fox jumps over the lazy dog"
            =~ Hashtbl.hash "The quick brown fox jumps over the lazy dog" );
          ( __LOC__ >:: fun _ ->
            Array.init 100 (fun i -> String.make i 'a')
            |> Array.iter (fun x ->
-                  Bs_hash_stubs.hash_string x =~ Hashtbl.hash x) );
-         ( __LOC__ >:: fun _ ->
-           (* only stamp matters here *)
-           hash {stamp = 1; name = "xx"; flags = 0}
-           =~ Bs_hash_stubs.hash_small_int 1;
-           hash {stamp = 11; name = "xx"; flags = 0}
-           =~ Bs_hash_stubs.hash_small_int 11 );
+                  Ext_platform_primitives.hash_string x =~ Hashtbl.hash x) );
          ( __LOC__ >:: fun _ ->
            (* only string matters here *)
            hash {stamp = 0; name = "Pervasives"; flags = 0}
-           =~ Bs_hash_stubs.hash_string "Pervasives";
+           =~ Ext_platform_primitives.hash_string "Pervasives";
            hash {stamp = 0; name = "UU"; flags = 0}
-           =~ Bs_hash_stubs.hash_string "UU" );
+           =~ Ext_platform_primitives.hash_string "UU" );
          ( __LOC__ >:: fun _ ->
            let v = Array.init 20 (fun i -> i) in
            let u = Array.init 30 (fun i -> 0 - i) in
-           Bs_hash_stubs.int_unsafe_blit v 0 u 10 20;
+           Ext_platform_primitives.int_unsafe_blit v 0 u 10 20;
            OUnit.assert_equal u
              (Array.init 30 (fun i -> if i < 10 then -i else i - 10)) );
        ]