From b0c5f42419f49f6677c1632ed89f26170c641a13 Mon Sep 17 00:00:00 2001
From: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Date: Sun, 9 Aug 2026 16:30:58 +0200
Subject: [PATCH] Replace CPPO browser branches with platform modules

Replace BROWSER conditionals with Dune-selected ordinary modules. The browser profile selects playground implementations while every other profile selects native implementations, keeping dev and release builds functionally identical and documenting the convention where it is applied.

Keep the platform boundary narrow: native builds use C primitives and artifact persistence, while the playground uses JavaScript-compatible primitives and no-op persistence. Keep shared Cmt_format behavior in an ordinary module and use generated source rules instead of virtual libraries, which trigger a Dune internal error with the compiler's unwrapped libraries and break @check and ocaml-lsp.

Remove CPPO from compiler sources that no longer need preprocessing, remove the unused hash_small_int test hook, and retain CPPO only for genuine type-specialization templates. Update architecture guidance and the error-variant catalog for the new source layout.

Signed-off-by: Cristiano Calcagno <cristianoc@users.noreply.github.com>
---
 AGENTS.md                                     |   9 +
 CHANGELOG.md                                  |   1 +
 CONTRIBUTING.md                               |  20 +-
 compiler/core/build_artifact_stubs.c          |  33 ++
 compiler/core/dune                            |  50 +-
 compiler/core/js_name_of_module_id.cppo.ml    | 167 ------
 compiler/core/lam_compile_main.cppo.ml        | 399 -------------
 compiler/core/lam_compile_main.ml             | 348 ++++++++++++
 compiler/core/lam_module_ident.ml             |   4 +-
 .../core/platform/native/build_artifact.ml    |   2 +
 .../platform/native/js_name_of_module_id.ml   | 139 +++++
 .../platform/playground/build_artifact.ml     |   2 +
 .../playground/js_name_of_module_id.ml        |   6 +
 compiler/dune                                 |  11 +-
 compiler/ext/bs_hash_stubs.cppo.ml            |  40 --
 compiler/ext/dune                             |  64 +--
 ...tubs.c => ext_platform_primitives_stubs.c} |  94 +---
 compiler/ext/ext_string.cppo.ml               | 530 ------------------
 compiler/ext/ext_string.ml                    | 469 ++++++++++++++++
 .../{ext_string.cppo.mli => ext_string.mli}   | 133 ++---
 compiler/ext/{ext_sys.cppo.ml => ext_sys.ml}  |  12 +-
 compiler/ext/hash.cppo.ml                     |   7 +-
 compiler/ext/hash_set.cppo.ml                 |   7 +-
 compiler/ext/hash_set_ident_mask.ml           |   3 +-
 ...eserved_map.cppo.ml => js_reserved_map.ml} | 305 +++++-----
 compiler/ext/ordered_hash_map.cppo.ml         |   3 +-
 .../native/ext_platform_primitives.ml         |  19 +
 .../playground/ext_platform_primitives.ml     |  13 +
 compiler/ext/vec.cppo.ml                      |   2 +-
 compiler/ml/cmt_format.ml                     |   6 +
 compiler/ml/cmt_format.mli                    |   2 +-
 ...mt_format.cppo.ml => cmt_format_common.ml} | 181 +++---
 compiler/ml/dune                              |  32 +-
 .../platform/native/cmt_format_persistence.ml |  52 ++
 .../playground/cmt_format_persistence.ml      |   2 +
 tests/ERROR_VARIANTS.md                       |   4 +-
 tests/ounit_tests/ounit_hash_stubs_test.ml    |  25 +-
 37 files changed, 1489 insertions(+), 1707 deletions(-)
 create mode 100644 compiler/core/build_artifact_stubs.c
 delete mode 100644 compiler/core/js_name_of_module_id.cppo.ml
 delete mode 100644 compiler/core/lam_compile_main.cppo.ml
 create mode 100644 compiler/core/lam_compile_main.ml
 create mode 100644 compiler/core/platform/native/build_artifact.ml
 create mode 100644 compiler/core/platform/native/js_name_of_module_id.ml
 create mode 100644 compiler/core/platform/playground/build_artifact.ml
 create mode 100644 compiler/core/platform/playground/js_name_of_module_id.ml
 delete mode 100644 compiler/ext/bs_hash_stubs.cppo.ml
 rename compiler/ext/{ext_basic_hash_stubs.c => ext_platform_primitives_stubs.c} (59%)
 delete mode 100644 compiler/ext/ext_string.cppo.ml
 create mode 100644 compiler/ext/ext_string.ml
 rename compiler/ext/{ext_string.cppo.mli => ext_string.mli} (71%)
 rename compiler/ext/{ext_sys.cppo.ml => ext_sys.ml} (85%)
 rename compiler/ext/{js_reserved_map.cppo.ml => js_reserved_map.ml} (52%)
 create mode 100644 compiler/ext/platform/native/ext_platform_primitives.ml
 create mode 100644 compiler/ext/platform/playground/ext_platform_primitives.ml
 create mode 100644 compiler/ml/cmt_format.ml
 rename compiler/ml/{cmt_format.cppo.ml => cmt_format_common.ml} (52%)
 create mode 100644 compiler/ml/platform/native/cmt_format_persistence.ml
 create mode 100644 compiler/ml/platform/playground/cmt_format_persistence.ml

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)) );
        ]