js_dump.ml

(* BuckleScript compiler
 * Copyright (C) 2015-2016 Bloomberg Finance L.P.
 * http://www.ocsigen.org/js_of_ocaml/
 * Copyright (C) 2010 Jérôme Vouillon
 * Laboratoire PPS - CNRS Université Paris Diderot
 *
 * 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, with linking exception;
 * either version 2.1 of the License, or (at your option) any 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.
*)
(* Authors: Jérôme Vouillon, Hongbo Zhang  *)
#if OCAML_VERSION =~ ">4.03.0" then
[@@@ocaml.warning "-57"] (* turn off such warning temporarily*)
#end
(*
  http://stackoverflow.com/questions/2846283/what-are-the-rules-for-javascripts-automatic-semicolon-insertion-asi
  ASI catch up
   {[
     a=b
       ++c
       ---
       a=b ++c
     ====================
     a ++
     ---
     a
     ++
     ====================
     a --
     ---
     a
     --
     ====================
     (continue/break/return/throw) a
     ---
     (continue/break/return/throw)
       a
     ====================
   ]}

*)


module P = Ext_pp
module E = Js_exp_make
module S = Js_stmt_make

module L = Js_dump_lit

(* There modules are dynamically inserted in the last stage
  {Caml_curry}
  {Caml_block}
  {Caml_option}

  They can appear anywhere so even if you have a module 
  {
    let module Caml_block = ...

    (* Later would insert the use of Caml_block here which should 
      point tto the runtime module
    *)
  }
  There are no sane way to easy detect it ahead of time, we should be
  conservative here.
  (our call Js_fun_env.get_unbounded env) is not precise
*)


module Curry_gen = struct 
  let pp_curry_dot f =   
    P.string f Js_runtime_modules.curry;
    P.string f L.dot 
  let pp_optimize_curry (f : P.t) (len : int) = 
    pp_curry_dot f;
    P.string f "__";
    P.string f (Printf.sprintf "%d" len)

  let pp_app_any (f : P.t) =    
    pp_curry_dot f;
    P.string f "app"

  let pp_app (f : P.t) (len : int) =    
    pp_curry_dot f;
    P.string f "_"; 
    P.string f (Printf.sprintf "%d" len)
end 

let block_dot f = 
  P.string f Js_runtime_modules.block;
  P.string f L.dot 

let pp_block_create f =   
  block_dot f ;
  P.string f L.caml_block_create

let dbg_block_dot f =   
  P.string f Js_runtime_modules.caml_chrome_block;
  P.string f L.dot 

let dbg_block_create f =   
  dbg_block_dot f ;
  P.string f L.caml_block_create



let dbg_poly_var f =   
  dbg_block_dot f;
  P.string f L.block_poly_var

let dbg_simple_variant f =   
  dbg_block_dot f ;
  P.string f L.block_simple_variant

let dbg_variant f =   
  dbg_block_dot f ; 
  P.string f L.block_variant



let return_indent = String.length L.return / Ext_pp.indent_length

let throw_indent = String.length L.throw / Ext_pp.indent_length

type cxt = Ext_pp_scope.t

let semi f = P.string f L.semi
let comma f = P.string f L.comma

let rec iter_lst cxt (f : P.t) ls element inter = 
  match ls with 
  | [] -> cxt 
  | [e] -> element cxt f e 
  | e::r -> 
    let acxt = element cxt f e  in 
    inter f; 
    iter_lst acxt f r element inter

let raw_snippet_exp_simple_enough (s : string) =
  Ext_string.for_all s (fun c -> 
  match c with 
  | 'a' .. 'z' | 'A' .. 'Z' | '_' -> true 
  | _ -> false
  )
(* Parentheses are required when the expression
   starts syntactically with "{" or "function"
   TODO:  be more conservative, since Google Closure will handle
   the precedence correctly, we also need people read the code..
   Here we force parens for some alien operators

   If we move assign into a statement, will be less?
   TODO: construct a test case that do need parenthesisze for expression
   IIE does not apply (will be inlined?)
*)

(* e = function(x){...}(x);  is good
*)        
let exp_need_paren  (e : J.expression) =
  match e.expression_desc with
  | Call ({expression_desc = Fun _ | Raw_js_function _; },_,_) -> true
  (* | Caml_uninitialized_obj _  *)
  | Raw_js_code (_, Exp)
  | Fun _ 
  | Raw_js_function _ 
  | Caml_block (_,_,_, (Blk_record _ | Blk_module _))
  | Object _ -> true
  | Raw_js_code (_,Stmt)
  | Length _
  | Call _
  | Caml_block_tag _
  | Seq _
  | Static_index _
  | Cond _
  | Bin _
  | Is_null_or_undefined _
  | String_index _
  | Array_index _
  | String_append _
  | Char_of_int _
  | Char_to_int _
  | Var _
  | Undefined
  | Null
  | Str _
  | Unicode _
  | Array _
  | Optional_block _
  | Caml_block  _
  | FlatCall _
  | Typeof _
  | Number _
  | Js_not _
  | Bool _
  | New _
    -> false

let comma_strings f ls =     
  iter_lst 
  () f 
  ls 
  (fun _ f  a  -> P.string f a )
  comma


let comma_idents (cxt: cxt) f ls =     
  iter_lst cxt f ls   
  Ext_pp_scope.ident
  comma

let pp_paren_params 
    (inner_cxt : cxt) (f : Ext_pp.t) 
    (lexical : Ident.t list) : unit =   
  P.string f L.lparen;
  let _ : cxt =  comma_idents inner_cxt f lexical in 
  P.string f L.rparen

(** Print as underscore for unused vars, may not be 
    needed in the future *)  
let ipp_ident cxt f id (un_used : bool) =
  Ext_pp_scope.ident cxt f (
    if un_used then
      Ext_ident.make_unused () 
    else
      id)

let pp_var_assign cxt f id  =       
  P.string f L.var ; 
  P.space f ; 
  let acxt = Ext_pp_scope.ident cxt f id in 
  P.space f ; 
  P.string f L.eq ; 
  P.space f ;
  acxt 

let pp_js_function_params_body f s params =   
  P.paren_group f 1 (fun _ ->
      comma_strings f params
    );
  P.brace f (fun _ -> P.string f s)

let pp_var_assign_this cxt f id =   
  let cxt = pp_var_assign cxt f id in 
  P.string f L.this;
  P.space f ;
  semi f ;
  P.newline f ;
  cxt 

let pp_var_declare cxt f id = 
  P.string f L.var ; 
  P.space f ; 
  let acxt = Ext_pp_scope.ident cxt f id in 
  semi f ;
  acxt 

let pp_direction f (direction : J.for_direction) =   
  match direction with
  | Upto -> P.string f L.plus_plus
  | Downto -> P.string f L.minus_minus 

let return_sp f = 
    P.string f L.return ; P.space f   

let bool f b =     
  P.string f (if b then  L.true_ else L.false_)

let comma_sp f =   
  comma f ; P.space f 
let comma_nl f = 
  comma f ; P.newline f 

let drop_comment (x : J.expression) = 
  if x.comment = None then x 
  else {x with comment = None}  
let debugger_nl f =   
  P.newline f ; 
  P.string f L.debugger;
  semi f ;
  P.newline f 

let break_nl f =   
  P.string f L.break;
  P.space f ;
  semi f;
  P.newline f

let continue f s =   
  P.string f L.continue;
  P.space f ;
  P.string f s;
  semi f

let formal_parameter_list cxt f offset l env  = 
    iter_lst cxt f l Ext_pp_scope.ident comma_sp 
(* IdentMap *)
(*
f/122 -->
  f/122 is in the map
  if in, use the old mapping
  else
    check  f,
     if in last bumped id
     else
        use "f", register it

  check "f"
         if not , use "f", register stamp -> 0
         else
           check stamp
             if in  use it
             else check last bumped id, increase it and register
*)
type name =
  | No_name
  | Name_top  of Ident.t
  | Name_non_top of Ident.t


(**
   Turn [function f (x,y) { return a (x,y)} ] into [Curry.__2(a)],
   The idea is that [Curry.__2] will guess the arity of [a], if it does
   hit, then there is no cost when passed
*)

let is_var (b : J.expression)  a = 
  match b.expression_desc with 
  | Var (Id i) -> Ident.same i a 
  | _ -> false

(* TODO: refactoring
   Note that {!pp_function} could print both statement and expression when [No_name] is given
*)
let rec
  try_optimize_curry cxt f len function_id =
  Curry_gen.pp_optimize_curry f len ; 
  P.paren_group f 1 (fun _ -> expression ~level:1 cxt f function_id  )


and  pp_function is_method
    cxt (f : P.t) ?(name=No_name)  (return : bool)
    (l : Ident.t list) (b : J.block) (env : Js_fun_env.t ) : cxt =
  match b, (name,  return)  with
  | [ {statement_desc =
         Return {return_value =
                   {expression_desc =
                      Call(({expression_desc = Var v ; _} as function_id),
                           ls ,
                           {arity = ( Full | NA as arity(* see #234*));
                            (* TODO: need a case to justify it*)
                            call_info =
                              (Call_builtin_runtime | Call_ml )})}}}],
    ((_, false) | (No_name, true))
    when
      (* match such case:
         {[ function(x,y){ return u(x,y) } ]}
         it can be optimized in to either [u] or [Curry.__n(u)]
      *)
      not is_method &&
      Ext_list.for_all2_no_exn ls l  is_var  ->
    let optimize  len p cxt f v =
      if p then try_optimize_curry cxt f len function_id
      else
        vident cxt f v in
    let len = List.length l in (* length *)
    (match name with
     | Name_top i | Name_non_top i  ->       
       let cxt = pp_var_assign cxt f i in 
       let cxt = optimize len (arity = NA && len <= 8) cxt f v in
       semi f ;
       cxt
     | No_name ->
       if return then 
         return_sp f ;
       optimize len (arity = NA && len <=8) cxt f v)

  | _, _  ->
    let set_env : Ident_set.t = (** identifiers will be printed following*)
      match name with
      | No_name ->
        Js_fun_env.get_unbounded env
      | Name_top id | Name_non_top id -> 
        Ident_set.add (Js_fun_env.get_unbounded env ) id in
    (* the context will be continued after this function *)
    let outer_cxt = Ext_pp_scope.merge cxt set_env in

    (* the context used to be printed inside this function

       when printing a function,
       only the enclosed variables and function name matters,
       if the function does not capture any variable, then the context is empty
    *)
    let inner_cxt = Ext_pp_scope.sub_scope outer_cxt set_env in
    let param_body () : unit =
      if is_method then
        match l with 
        | [] -> assert false 
        | this::arguments -> 
          let cxt = P.paren_group f 1 (fun _ ->
              formal_parameter_list inner_cxt  f 1 arguments env )
          in
          P.space f ;
          P.brace_vgroup f 1 (fun _ ->
              let cxt =
                if Js_fun_env.get_unused env 0 then cxt 
                else  pp_var_assign_this cxt f this in
              function_body cxt f b
            );
      else 
        let cxt = 
          P.paren_group f 1 (fun _ -> formal_parameter_list inner_cxt  f 0 l env ) in
        P.space f ;
        P.brace_vgroup f 1 (fun _ -> function_body cxt f b ) 
    in
    let lexical : Ident_set.t = Js_fun_env.get_lexical_scope env in
    let enclose  lexical  return =
      let handle lexical =
        if  Ident_set.is_empty lexical
        then
          (if return then
             return_sp f ;
           match name with
           | No_name ->
             (* see # 1692, add a paren for annoymous function for safety  *)
             P.paren_group f 1  (fun _ ->
                 P.string f L.function_;
                 P.space f ;
                 param_body ())                
           | Name_non_top x  ->
             ignore (pp_var_assign inner_cxt f x : cxt ); 
             P.string f L.function_;
             P.space f ;
             param_body ();
             semi f 
           | Name_top x  ->
             P.string f L.function_;
             P.space f ;
             ignore (Ext_pp_scope.ident inner_cxt f x : cxt);
             param_body ())
        else
          (* print as
             {[(function(x,y){...} (x,y))]}
          *)
          let lexical = Ident_set.elements lexical in
          (if return then 
             return_sp f             
           else
             match name with
             | No_name -> ()
             | Name_non_top name | Name_top name->
               ignore (pp_var_assign inner_cxt f name : cxt)
          )
          ;
          P.string f L.lparen;
          P.string f L.function_;
          pp_paren_params inner_cxt f lexical; 
          P.brace_vgroup f 0  (fun _ ->
              return_sp f;
              P.string f L.function_;
              P.space f ;
              (match name with
               | No_name  -> ()
               | Name_non_top x | Name_top x -> ignore (Ext_pp_scope.ident inner_cxt f x));
              param_body ());
          pp_paren_params inner_cxt f lexical;     
          P.string f L.rparen;
          match name with
          | No_name -> () (* expression *)
          | _ -> semi f (* has binding, a statement *)  in
      handle 
        (match name with
         | Name_top name | Name_non_top name  when Ident_set.mem lexical name ->
           (*TODO: when calculating lexical we should not include itself *)
           Ident_set.remove lexical name
         | _ -> lexical) in
    enclose lexical return;
    outer_cxt


(* Assume the cond would not change the context,
    since it can be either [int] or [string]
*)
and pp_one_case_clause : 'a .
  _ -> P.t -> (P.t -> 'a -> unit) -> 'a J.case_clause -> _
  = fun cxt f  pp_cond
    ({switch_case; switch_body ; should_break; comment; } : _ J.case_clause) ->
    let cxt =
      P.group f 1  (fun _ ->
          P.group f 1 (fun _ ->
              P.string f L.case;
              P.space f ;
              pp_comment_option f comment;
              pp_cond  f switch_case; (* could be integer or string *)
              P.space f ;
              P.string f L.colon  );
          P.group f 1 (fun _ ->
              let cxt =
                match switch_body with
                | [] -> cxt
                | _ ->
                  P.newline f ;
                  statement_list false cxt  f switch_body
              in
              (if should_break then
                 begin
                   P.newline f ;
                   P.string f L.break;
                   semi f;
                 end) ;
              cxt))
    in
    P.newline f;
    cxt

and loop_case_clauses  :  'a . cxt ->
  P.t -> (P.t -> 'a -> unit) -> 'a J.case_clause list -> cxt
  = fun  cxt  f pp_cond cases ->
    Ext_list.fold_left cases cxt (fun acc x -> pp_one_case_clause acc f pp_cond x)              

and vident cxt f  (v : J.vident) =
  match v with
  | Id v | Qualified(v, _, None) ->
    Ext_pp_scope.ident cxt f v
  | Qualified (id, (Ml | Runtime),  Some name) ->
    let cxt = Ext_pp_scope.ident cxt f id in
    P.string f L.dot;
    P.string f (Ext_ident.convert  name);
    cxt
  | Qualified (id, External _, Some name) ->
    let cxt = Ext_pp_scope.ident cxt f id in
    Js_dump_property.property_access f name ;
    cxt

(* The higher the level, the more likely that inner has to add parens *)
and expression ~level:l cxt  f (exp : J.expression) : cxt =
  pp_comment_option f exp.comment ;
  expression_desc cxt ~level:l f exp.expression_desc

and expression_desc cxt ~(level:int) f x : cxt  =
  match x with
  | Null ->
    P.string f L.null; cxt 
  | Undefined -> 
    P.string f L.undefined; cxt 
  | Var v ->
    vident cxt f v
  | Bool b ->
    bool f b ; cxt
  | Seq (e1, e2) ->
    P.cond_paren_group f (level > 0) 1 (fun () ->
      let cxt = expression ~level:0 cxt f e1 in
      comma_sp f;
      expression ~level:0 cxt f e2 )
  | Fun (method_, l, b, env) ->  (* TODO: dump for comments *)
    pp_function method_ cxt f false  l b env
  (* TODO:
     when [e] is [Js_raw_code] with arity
     print it in a more precise way
     It seems the optimizer already did work to make sure
     {[
       Call (Raw_js_code (s, Exp i), el, {Full})
       when Ext_list.length_equal el i
     ]}
  *)

  | Call (e, el, info) ->
    P.cond_paren_group f (level > 15) 1  (fun _ -> 
      P.group f 1 (fun _ ->
          match info, el  with
          | {arity  = Full }, _
          | _, [] ->
            let cxt = expression ~level:15 cxt f e in
            P.paren_group f 1 (fun _ -> arguments cxt  f el )

          | _ , _ ->
            let len = List.length el in
            if 1 <= len && len <= 8 then
              begin
                Curry_gen.pp_app f len ; 
                P.paren_group f 1 (fun _ -> arguments cxt f (e::el))
              end
            else
              begin
                Curry_gen.pp_app_any f ;
                P.paren_group f 1
                  (fun _ -> arguments cxt f [ e ; E.array Mutable el])
              end))
  | FlatCall(e,el) ->
    P.group f 1 (fun _ ->
        let cxt = expression ~level:15 cxt f e in
        P.string f L.dot;
        P.string f L.apply;
        P.paren_group f 1 (fun _ ->
            P.string f L.null;
            comma_sp f ;
            expression ~level:1 cxt f el
          )
      )
  | Char_to_int e ->
    (match e.expression_desc with
     | String_index (a,b) ->
       P.group f 1 (fun _ ->
           let cxt = expression ~level:15 cxt f a in
           P.string f L.dot;
           P.string f L.char_code_at;
           P.paren_group f 1 (fun _ -> expression ~level:0 cxt f b);
         )
     | _ ->
       P.group f 1 (fun _ ->
           let cxt = expression ~level:15 cxt f e in
           P.string f L.dot;
           P.string f L.char_code_at;
           P.string f "(0)";
           cxt))
  | Char_of_int e ->
    P.group f 1 (fun _ ->
        P.string f L.string_cap;
        P.string f L.dot;
        P.string f L.fromCharcode;
        P.paren_group f 1 (fun _ -> arguments cxt f [e])
      )  
  | Unicode s ->
    P.string f "\"";
    P.string f s ;
    P.string f "\"";
    cxt
  | Str (_, s) ->
    (*TODO --
       when utf8-> it will not escape '\\' which is definitely not we want
    *)
    Js_dump_string.pp_string f  s;
    cxt
  | Raw_js_function (s,params) ->   
    P.string f L.function_; 
    P.space f ; 
    pp_js_function_params_body f s params;
    cxt 
  | Raw_js_code (s,info) ->
    (match info with
     | Exp ->
       if raw_snippet_exp_simple_enough s then 
         P.string f s        
       else begin 
         P.string f L.lparen;
         P.string f s ;
         P.string f L.rparen;
       end;
       cxt
     | Stmt ->
       P.newline f  ;
       P.string f s ;
       P.newline f ;
       cxt)
  
  | Number v ->
    let s =
      match v with
      | Float {f} ->
        Js_number.caml_float_literal_to_js_string f
      (* attach string here for float constant folding?*)
      | Int { i; _}
        -> Int32.to_string i (* check , js convention with ocaml lexical convention *)
      | Uint i
        -> Format.asprintf "%lu" i
      | Nint i -> Nativeint.to_string i in
    let need_paren =
      if s.[0] = '-'
      then level > 13  (* Negative numbers may need to be parenthesized. *)
      else level = 15  (* Parenthesize as well when followed by a dot. *)
           && s.[0] <> 'I' (* Infinity *)
           && s.[0] <> 'N' (* NaN *) in
    let action = 
      fun _ -> P.string f s  in
    (
      if need_paren
      then P.paren f  action
      else action ()
    );
    cxt
  | Is_null_or_undefined e ->
    P.cond_paren_group f (level > 0) 1 (fun _ ->
        let cxt = expression ~level:1 cxt f e in
        P.space f ;
        P.string f "==";
        P.space f ;
        P.string f L.null;
        cxt)  
  | Js_not e ->
    P.cond_paren_group f (level > 13) 1 (fun _ -> 
      P.string f "!" ;
      expression ~level:13 cxt f e
    )
  | Typeof e
    ->
    P.string f "typeof";
    P.space f;
    expression ~level:13 cxt f e
 
  | Bin (Eq, ({expression_desc = Array_index({expression_desc = Var i; _},
                                       {expression_desc = Number (Int {i = k0 })}
                                      ) } as lhs),
         {expression_desc =
            (Bin((Plus as op),
                 {expression_desc = Array_index(
                      {expression_desc = Var j; _},
                      {expression_desc = Number (Int {i = k1; })}
                    ); _}, delta)
            | Bin((Plus as op), delta,
                  {expression_desc = Array_index(
                       {expression_desc = Var j; _},
                       {expression_desc = Number (Int {i = k1; })}
                     ); _})
            | Bin((Minus as op),
                  {expression_desc = Array_index(
                       {expression_desc = Var j; _},
                       {expression_desc = Number (Int {i = k1; })}
                     ); _}, delta)

            )})
    when  k0 = k1 && Js_op_util.same_vident i j
    (* Note that
       {[x = x + 1]}
       is exactly the same  (side effect, and return value)
       as {[ ++ x]}
       same to
       {[ x = x + a]}
       {[ x += a ]}
       they both return the modified value too
    *)
    (* TODO:
       handle parens..
    *)
    ->
    (** TODO: parenthesize when necessary *)
    (match delta, op with
     | {expression_desc = Number (Int { i =  1l; _})}, Plus
     | {expression_desc = Number (Int { i =  -1l; _})}, Minus
       ->
       P.string f L.plusplus;
       P.space f ;
       expression ~level:13 cxt f lhs (* Static index level is 15*)
     | {expression_desc = Number (Int { i =  -1l; _})}, Plus
     | {expression_desc = Number (Int { i =  1l; _})}, Minus
       ->
       P.string f L.minusminus;
       P.space f ;
       expression ~level:13 cxt f lhs
       
     | _, _ ->
       let cxt = expression ~level:13 cxt f lhs in
       P.space f ;
       P.string f (if op = Plus then "+=" else "-=");
       P.space f ;
       expression ~level:13 cxt  f delta) 


  | Bin (Minus, {expression_desc = Number (Int {i=0l;_} | Float {f = "0."})}, e)
    (* TODO:
       Handle multiple cases like
       {[ 0. - x ]}
       {[ 0.00 - x ]}
       {[ 0.000 - x ]}
    *)
    ->
    P.cond_paren_group f (level > 13 ) 1 (fun _ -> 
      P.string f "-" ;
      expression ~level:13 cxt f e
    )
  | Bin (op, e1, e2) ->
    let (out, lft, rght) = Js_op_util.op_prec op in
    let need_paren =
      level > out || (match op with Lsl | Lsr | Asr -> true | _ -> false) in
    (* We are more conservative here, to make the generated code more readable
          to the user *)
    P.cond_paren_group f need_paren 1  (fun _ -> 
      let cxt = expression ~level:lft cxt  f e1 in
      P.space f;
      P.string f (Js_op_util.op_str op);
      P.space f;
      expression ~level:rght cxt   f e2)
  | String_append (e1, e2) ->
    let op : Js_op.binop = Plus in
    let (out, lft, rght) = Js_op_util.op_prec op in
    let need_paren =
      level > out || (match op with Lsl | Lsr | Asr -> true | _ -> false) in
    P.cond_paren_group f need_paren 1 (fun _ -> 
      let cxt = expression  ~level:lft cxt f e1 in
      P.space f ;
      P.string f "+";
      P.space f;
      expression  ~level:rght cxt   f e2)
  | Array (el,_) ->
    (** TODO: simplify for singleton list *)
      (match el with
      | []| [ _ ] -> P.bracket_group f 1 (fun _ -> array_element_list  cxt f el)
      | _ -> P.bracket_vgroup f 1 (fun _ -> array_element_list  cxt f el))
  | Optional_block (e,identity) -> 
    expression ~level cxt f  
      (if identity then e 
       else       
         E.runtime_call Js_runtime_modules.option "some" [e])
  | Caml_block(el,_, _, Blk_module fields) ->        
      expression_desc cxt ~level f (Object (
        (Ext_list.map_combine fields el Ext_ident.convert)))
  | Caml_block(el,_, _, Blk_record fields) ->        
      expression_desc cxt ~level f (Object (
        (List.combine (Array.to_list fields) el )))      
        (* name convention of Record is slight different from modules 
        *)
  | Caml_block( el, mutable_flag, tag, tag_info)
    ->
    (* Note that, if we ignore more than tag [0] we loose some information
       with regard tag  

       TODO: for numbers like 248, 255 we can reverse engineer to make it
         [Obj.xx_flag], but we can not do this in runtime libraries

       When it does not need block runtime, it means it will be compiled 
       as an array, note exception or open variant it is outer-most is 
       simply an array
    *)
    if not !Js_config.debug then begin 
      if not (Js_block_runtime.needBlockRuntime tag tag_info) then 
        expression_desc cxt ~level f  (Array (el, mutable_flag))
      else  
        begin
          pp_block_create f;
          P.paren_group f 1 (fun _ -> arguments cxt f [tag; E.array mutable_flag el])
        end  
    end 
      else
        if not (Js_block_runtime.needChromeRuntime tag tag_info) then 
          expression_desc cxt ~level f  (Array (el, mutable_flag))
        else 
      (  
        match tag_info with 
        | Blk_record _ 
        | Blk_module _ 
        | Blk_module_export -> 
          assert false 
            (* 
              This can not happen, see the pattern match on previous branch 
              TODO: we still need clean up local module compilation 
              to make it more obvious
            *)
        | Blk_variant name ->  
          dbg_poly_var f;
          P.paren_group f 1 (fun _ -> arguments cxt f [ 
              E.str name;
              E.array mutable_flag el])        
        | Blk_constructor(name,number) 

          -> (* has to be debug mode *)          
          if number = 1 && Js_block_runtime.tag_is_zero tag then 
            begin
              dbg_simple_variant f; 
              P.paren_group f 1 (fun _ ->
                  arguments cxt f 
                    [E.str name; E.array mutable_flag el])             
            end
          else begin 
            dbg_variant f;
            P.paren_group f 1 (fun _ ->
                arguments cxt f 
                  [E.str name; tag; E.array mutable_flag el])
          end

          
#if OCAML_VERSION =~ ">4.03.0" then                               
        | Blk_record_inlined _ (* TODO: No support for debug mode yet *)
#end
        | Blk_tuple
        | Blk_extension
        | Blk_class
        | Blk_array
#if OCAML_VERSION =~ ">4.03.0" then     
        | Blk_record_ext _
#end      
        | Blk_extension_slot
        | Blk_na _
           ->           
          dbg_block_create f;
          P.paren_group f 1 (fun _ -> arguments cxt f [tag; E.array mutable_flag el])
    )

  | Caml_block_tag e ->
    P.group f 1 (fun _ ->
        let cxt = expression ~level:15 cxt f  e in
        P.string f L.dot ;
        P.string f L.tag ;
        cxt)
  | Array_index (e, p)
  | String_index (e,p)
    ->
    P.cond_paren_group f (level > 15) 1 (fun _ -> 
        P.group f 1  (fun _ ->
        let cxt = expression ~level:15 cxt f e in
        P.bracket_group f 1 (fun _ ->
        expression ~level:0 cxt f p )))  
  | Static_index (e, s,_) ->
    P.cond_paren_group f (level > 15) 1 (fun _ -> 
        let cxt = expression ~level:15 cxt f e in
        Js_dump_property.property_access f s ;
        (* See [ .obj_of_exports]
           maybe in the ast level we should have
           refer and export
        *)
        cxt) 

  | Length (e, _) ->
    (** Todo: check parens *)
    P.cond_paren_group f (level > 15) 1 (fun _ -> 
      let cxt = expression ~level:15 cxt f e in
      P.string f L.dot;
      P.string f L.length;
      cxt)
  | New (e,  el) ->
    P.cond_paren_group f (level > 15) 1 (fun _ ->
        P.group f 1 ( fun _ ->
            P.string f L.new_;
            P.space f;
            let cxt = expression ~level:16 cxt f e in
            P.paren_group f 1 (fun _ ->
                match el with
                | Some el  -> arguments cxt f el
                | None -> cxt)))
  | Cond (e, e1, e2) ->
    let action () =      
      let cxt =  expression ~level:3 cxt f e in
      P.space f;
      P.string f L.question;
      P.space f;
      (*
            [level 1] is correct, however
            to make nice indentation , force nested conditional to be parenthesized
          *)
      let cxt = P.group f 1 (fun _ -> expression ~level:3 cxt f e1) in

      P.space f;
      P.string f L.colon;
      P.space f ;
      (* idem *)
      P.group f 1 (fun _ -> expression ~level:3 cxt f e2)
    in
    if level > 2 then P.paren_vgroup f 1 action else action ()

  | Object lst ->
    match lst with
    | [] -> P.string f "{ }" ; cxt
    | _ ->
      let action () =
        P.brace_vgroup f 1 (fun _ ->
        property_name_and_value_list cxt f lst) in
      if level > 1 then
        (* #1946 object literal is easy to be
           interpreted as block statement
           here we avoid parens in such case
           {[
             var f = { x : 2 , y : 2}
           ]}
        *)
        P.paren_group f 1 action
      else action ()

and property_name_and_value_list cxt f (l : J.property_map) =     
  iter_lst cxt f l (fun cxt f (pn,e) -> 
    Js_dump_property.property_key f pn ;
    P.string f L.colon;
    P.space f;
    expression ~level:1 cxt f e
  ) comma_nl      

and array_element_list cxt f (el : E.t list) : cxt =
  iter_lst cxt f el (expression ~level:1) comma_nl
 
and arguments cxt f (l : E.t list) : cxt =
  iter_lst cxt f l (expression ~level:1) comma_sp
  
and variable_declaration top cxt f
    (variable : J.variable_declaration) : cxt =
  (* TODO: print [const/var] for different backends  *)
  match variable with
  | {ident = i; value =  None; ident_info ; _} ->
    if ident_info.used_stats = Dead_pure then cxt
    else pp_var_declare cxt f i 
  | { ident = name; value =  Some e; ident_info = {used_stats; _}} ->
    match used_stats with
    | Dead_pure ->
      cxt
    | Dead_non_pure ->
      (* Make sure parens are added correctly *)
      statement_desc top cxt f (J.Exp e)
    | _ ->
      match e.expression_desc, top  with
      | Fun (method_, params, b, env ), _ ->
        pp_function method_ cxt f
          ~name:(if top then Name_top name else Name_non_top name)
          false params b env      
      | Raw_js_function(s,params), true ->     
        P.string f L.function_;             
        P.space f ; 
        let acxt = Ext_pp_scope.ident cxt f name in 
        P.space f ; 
        pp_js_function_params_body f s params;
        semi f;
        acxt 
      | _, _ ->
        let cxt = pp_var_assign cxt f name in 
        let cxt = expression ~level:1 cxt f e in
        semi f;
        cxt

    
and ipp_comment : 'a . P.t -> 'a  -> unit = fun   f comment ->
  ()


(** don't print a new line -- ASI
    FIXME: this still does not work in some cases...
    {[
      return /* ... */
      [... ]
    ]}
*)

and pp_comment f comment =
  if String.length comment > 0 then
    begin
      P.string f "/* "; P.string f comment ; P.string f " */"
    end

and pp_comment_option f comment  =
  match comment with
  | None -> ()
  | Some x -> pp_comment f x
and statement top cxt f
    ({statement_desc = s;  comment ; _} : J.statement)  : cxt =

  pp_comment_option f comment ;
  statement_desc top cxt f s

and statement_desc top cxt f (s : J.statement_desc) : cxt =
  match s with
  | Block [] ->
    ipp_comment f  L.empty_block; (* debugging*)
    cxt
  | Exp {expression_desc = Var _;}
    -> (* Does it make sense to optimize here? *)
    semi f; cxt
  | Exp e ->
    let cxt =
      (
        if exp_need_paren  e
        then P.paren_group f 1
        else P.group f 0
      ) (fun _ -> expression ~level:0 cxt f e ) in
    semi f;
    cxt
  | Block b -> (* No braces needed here *)
    ipp_comment f L.start_block;
    let cxt = statement_list top cxt  f b in
    ipp_comment f  L.end_block;
    cxt
  | Variable l ->
    variable_declaration top cxt  f l

  | If (e, s1,  s2) -> (* TODO: always brace those statements *)
    P.string f L.if_;
    P.space f;
    let cxt = P.paren_group f 1 (fun _ -> expression ~level:0 cxt f e) in
    P.space f;
    let cxt = block cxt f s1 in
    (match s2 with
     | []
     | [{statement_desc = (Block [] | Exp {expression_desc = Var _;} ); }]
       -> P.newline f; cxt
     | [{statement_desc = If _} as nest]
     | [{statement_desc = Block [ {statement_desc = If _ ; _} as nest] ; _}]
       ->
       P.space f;
       P.string f L.else_;
       P.space f;
       statement false cxt f nest
     | (_::_) as s2 ->
       P.space f;
       P.string f L.else_;
       P.space f ;
       block  cxt f s2)
  | While (label, e, s, _env) ->  (*  FIXME: print scope as well *)
    begin
      (match label with
       | Some i ->
         P.string f i ;
         P.string f L.colon;
         P.newline f ;
       | None -> ());
      let cxt =
        match e.expression_desc with
        | Number (Int {i = 1l}) ->
          P.string f L.while_;
          P.string f L.lparen;
          P.string f L.true_;
          P.string f L.rparen;
          P.space f ;
          cxt
        | _ ->
          P.string f L.while_;
          let cxt = P.paren_group f 1 (fun _ ->  expression ~level:0 cxt f e) in
          P.space f ;
          cxt
      in
      let cxt = block cxt f s in
      semi f;
      cxt
    end
  | ForRange (for_ident_expression, finish, id, direction, s, env) ->
    let action cxt  =
      P.vgroup f 0 ( fun _ ->
          let cxt = P.group f 0 (fun _ ->
              (* The only place that [semi] may have semantics here *)
              P.string f L.for_ ;
              P.paren_group f 1 ( fun _ ->
                  let cxt, new_id =
                    match for_ident_expression, finish.expression_desc with
                    | Some ident_expression , (Number _ | Var _ ) ->
                      let cxt = pp_var_assign cxt f id in  
                      expression ~level:0 cxt f ident_expression, None
                    | Some ident_expression, _ ->
                      let cxt = pp_var_assign cxt f id in 
                      let cxt = expression ~level:1 cxt f ident_expression in
                      P.space f ;
                      comma f;  
                      let id = Ext_ident.create (Ident.name id ^ "_finish") in
                      let cxt = Ext_pp_scope.ident cxt f id in
                      P.space f ;
                      P.string f L.eq;
                      P.space f;
                      expression ~level:1 cxt f finish, Some id
                    | None, (Number _ | Var _) ->
                      cxt, None
                    | None , _ ->
                      let id = Ext_ident.create (Ident.name id ^ "_finish") in
                      let cxt = pp_var_assign cxt f id in 
                      expression ~level:15 cxt f finish, Some id in
                  semi f ;
                  P.space f;
                  let cxt = Ext_pp_scope.ident cxt f id in
                  P.space f;
                  let right_prec  =
                    match direction with
                    | Upto ->
                      let (_,_,right) = Js_op_util.op_prec Le  in
                      P.string f L.le;
                      right
                    | Downto ->
                      let (_,_,right) = Js_op_util.op_prec Ge in
                      P.string f L.ge ;
                      right
                  in
                  P.space f ;
                  let cxt  =
                    expression   ~level:right_prec cxt  f 
                      (match new_id with
                       | Some i -> E.var i
                       | None -> finish) in
                  semi f;
                  P.space f;
                  pp_direction f direction;
                  Ext_pp_scope.ident cxt f id)) in
          block  cxt f s ) in
    let lexical = Js_closure.get_lexical_scope env in
    if Ident_set.is_empty lexical
    then action cxt
    else
      (* unlike function,
         [print for loop] has side effect,
         we should take it out
      *)
      let inner_cxt = Ext_pp_scope.merge cxt lexical in
      let lexical = Ident_set.elements lexical in
      P.vgroup f 0
        (fun _ ->
           P.string f L.lparen;
           P.string f L.function_;               
           pp_paren_params inner_cxt f lexical; 
           let cxt = P.brace_vgroup f 0  (fun _ -> action inner_cxt) in               
           pp_paren_params inner_cxt f lexical; 
           P.string f L.rparen;
           semi f;
           cxt
        )
  | Continue s -> continue f s ; cxt
    (* P.newline f;  #2642 *)    
  | Debugger ->  debugger_nl f ; cxt
  | Break -> break_nl f; cxt

  | Return {return_value = e} ->
    begin match e.expression_desc with
      | Fun (method_,  l, b, env) ->
        let cxt =
          pp_function method_ cxt f true l b env in
        semi f ; cxt
      | Undefined ->  
        return_sp f;
        semi f;
        cxt 
      | _ ->
        return_sp f ;
        (* P.string f "return ";(\* ASI -- when there is a comment*\) *)
        P.group f return_indent (fun _ ->
            let cxt =  expression ~level:0 cxt f e in
            semi f;
            cxt)
        (* There MUST be a space between the return and its
           argument. A line return will not work *)
    end
  | Int_switch (e, cc, def) ->
    P.string f L.switch;
    P.space f;
    let cxt = P.paren_group f 1 (fun _ ->  expression ~level:0 cxt f e) in
    P.space f;
    P.brace_vgroup f 1 (fun _ ->
        let cxt = loop_case_clauses cxt f (fun f i -> P.string f (string_of_int i) ) cc in
        match def with
        | None -> cxt
        | Some def ->
          P.group f 1  (fun _ ->
              P.string f L.default;
              P.string f L.colon;
              P.newline f;
              statement_list  false cxt  f def))

  | String_switch (e, cc, def) ->
    P.string f L.switch;
    P.space f;
    let cxt = P.paren_group f 1 (fun _ ->  expression ~level:0 cxt f e) in
    P.space f;
    P.brace_vgroup f 1 (fun _ ->
        let cxt = loop_case_clauses cxt f Js_dump_string.pp_string  cc in
        match def with
        | None -> cxt
        | Some def ->
          P.group f 1 (fun _ ->
          P.string f L.default;
          P.string f L.colon;
          P.newline f;
          statement_list  false cxt  f def ))
  | Throw e ->
    P.string f L.throw;
    P.space f ;
    P.group f throw_indent  (fun _ ->
        let cxt = expression ~level:0 cxt f e in
        semi f ; cxt)

  (* There must be a space between the return and its
     argument. A line return would not work *)
  | Try (b, ctch, fin) ->
    P.vgroup f 0 (
      fun _->
        P.string f L.try_;
        P.space f ;
        let cxt = block cxt f b in
        let cxt =
          match ctch with
          | None ->
            cxt
          | Some (i, b) ->
            P.newline f;
            P.string f "catch (";
            let cxt = Ext_pp_scope.ident cxt f i in
            P.string f ")";
            block cxt f b in
        match fin with
        | None -> cxt
        | Some b ->
          P.group f 1 (fun _ ->
              P.string f L.finally;
              P.space f;
              block cxt f b))

and function_body (cxt : cxt) f (b : J.block) : unit =
  match b with
  | []     -> ()
  | [s]    ->
    begin match s.statement_desc with
    | If (bool,
          then_,
           [{
              statement_desc =
                Return {return_value = {expression_desc = Undefined}} }])
        ->
        ignore (statement false cxt f {s with statement_desc = If(bool,then_, [])} : cxt)
    | _ ->        
      ignore (statement false  cxt f  s : cxt)
    end
  | s :: r ->
    let cxt = statement false cxt f s in
    P.newline f;
    function_body cxt f  r

(* similar to [block] but no braces *)
and statement_list top cxt f  b =
  iter_lst cxt f b  (fun cxt f s -> statement top cxt f s )
    (if top then 
      (fun f -> P.newline f ; P.force_newline f )
      else P.newline
    )


and block cxt f b =
  (* This one is for '{' *)
  P.brace_vgroup f 1 (fun _ -> statement_list false cxt   f b )




let string_of_block  (block : J.block) =
  let buffer  = Buffer.create 50 in
  let f = P.from_buffer buffer in
  let _ : cxt =  statement_list true Ext_pp_scope.empty  f block in
  P.flush  f ();
  Buffer.contents buffer



let string_of_expression (e : J.expression) =
  let buffer  = Buffer.create 50 in
  let f = P.from_buffer buffer in
  let _ : cxt =  expression ~level:0  Ext_pp_scope.empty  f e in
  P.flush  f ();
  Buffer.contents buffer