From 6d44206fb229125af336e303e445923705184cdd Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 19 Aug 2020 02:20:57 -0700
Subject: [PATCH 1/8] Fix letop binary printing

this was happening after the downgrade so it effectively only worked if
you were printing to the console?
---
 src/reason-parser/reason_pprint_ast.ml        | 7 ++++---
 src/reason-parser/reason_syntax_util.cppo.ml  | 9 +++------
 src/reason-parser/reason_syntax_util.cppo.mli | 2 +-
 src/reason-parser/reason_toolchain_ocaml.ml   | 7 +++----
 src/refmt/reason_implementation_printer.ml    | 6 ------
 5 files changed, 11 insertions(+), 20 deletions(-)

diff --git a/src/reason-parser/reason_pprint_ast.ml b/src/reason-parser/reason_pprint_ast.ml
index 802e5d2e6..28f77b091 100644
--- a/src/reason-parser/reason_pprint_ast.ml
+++ b/src/reason-parser/reason_pprint_ast.ml
@@ -8313,9 +8313,10 @@ let add_explicit_arity_mapper super =
   { super with Ast_mapper. expr; pat }
 
 let preprocessing_mapper =
-  ml_to_reason_swap_operator_mapper
-    (escape_stars_slashes_mapper
-      (add_explicit_arity_mapper Ast_mapper.default_mapper))
+  backport_letopt_mapper
+    (ml_to_reason_swap_operator_mapper
+      (escape_stars_slashes_mapper
+        (add_explicit_arity_mapper Ast_mapper.default_mapper)))
 
 let core_type ppf x =
   format_layout ppf
diff --git a/src/reason-parser/reason_syntax_util.cppo.ml b/src/reason-parser/reason_syntax_util.cppo.ml
index 0e658279b..8cf869672 100644
--- a/src/reason-parser/reason_syntax_util.cppo.ml
+++ b/src/reason-parser/reason_syntax_util.cppo.ml
@@ -583,9 +583,9 @@ let remove_stylistic_attrs_mapper =
   remove_stylistic_attrs_mapper_maker Ast_mapper.default_mapper
 
 #if OCAML_VERSION >= (4, 8, 0)
-let noop_mapper =
+let noop_mapper super =
   let noop = fun _mapper x -> x in
-  { Ast_mapper.default_mapper with
+  { super with
     expr = noop;
     structure = noop;
     structure_item = noop;
@@ -608,7 +608,7 @@ let backport_letopt_mapper = noop_mapper
  *
  * (let+)((and+)(y, b), ((x, a)) => x + a)
  *)
-let backport_letopt_mapper_maker super =
+let backport_letopt_mapper super =
   let open Ast_408 in
   let open Ast_mapper in
 { super with
@@ -654,9 +654,6 @@ let backport_letopt_mapper_maker super =
         ])}
     | _ -> super.expr mapper expr
 }
-
-let backport_letopt_mapper =
-  backport_letopt_mapper_maker Ast_mapper.default_mapper
 #endif
 
 let escape_stars_slashes str =
diff --git a/src/reason-parser/reason_syntax_util.cppo.mli b/src/reason-parser/reason_syntax_util.cppo.mli
index f90549927..05f46298a 100644
--- a/src/reason-parser/reason_syntax_util.cppo.mli
+++ b/src/reason-parser/reason_syntax_util.cppo.mli
@@ -38,7 +38,7 @@ val isLineComment : string -> bool
 
 val remove_stylistic_attrs_mapper : Ast_mapper.mapper
 
-val backport_letopt_mapper : Ast_mapper.mapper
+val backport_letopt_mapper : Ast_mapper.mapper -> Ast_mapper.mapper
 
 val escape_stars_slashes : string -> string
 
diff --git a/src/reason-parser/reason_toolchain_ocaml.ml b/src/reason-parser/reason_toolchain_ocaml.ml
index 249751171..3700019ec 100644
--- a/src/reason-parser/reason_toolchain_ocaml.ml
+++ b/src/reason-parser/reason_toolchain_ocaml.ml
@@ -136,10 +136,9 @@ let format_interface_with_comments (signature, _) formatter =
     (To_current.copy_signature signature)
 let format_implementation_with_comments (structure, _) formatter =
   let structure =
-    Reason_syntax_util.(apply_mapper_to_structure structure remove_stylistic_attrs_mapper)
-  in
-  let structure =
-    Reason_syntax_util.(apply_mapper_to_structure structure backport_letopt_mapper)
+    Reason_syntax_util.(apply_mapper_to_structure
+      structure
+      (backport_letopt_mapper remove_stylistic_attrs_mapper))
   in
   Pprintast.structure formatter
     (To_current.copy_structure structure)
diff --git a/src/refmt/reason_implementation_printer.ml b/src/refmt/reason_implementation_printer.ml
index 6558dd153..b945aa8d4 100644
--- a/src/refmt/reason_implementation_printer.ml
+++ b/src/refmt/reason_implementation_printer.ml
@@ -53,16 +53,10 @@ let print printtype filename parsedAsML output_chan output_formatter =
     let ast =
       Reason_syntax_util.(apply_mapper_to_structure ast remove_stylistic_attrs_mapper)
     in
-    let ast =
-      Reason_syntax_util.(apply_mapper_to_structure ast backport_letopt_mapper)
-    in
     Ast_io.to_channel output_chan filename
       (Ast_io.Impl ((module OCaml_current),
                     Reason_toolchain.To_current.copy_structure ast))
   | `AST -> fun (ast, _) -> (
-    let ast =
-      Reason_syntax_util.(apply_mapper_to_structure ast backport_letopt_mapper)
-    in
     Printast.implementation output_formatter
       (Reason_toolchain.To_current.copy_structure ast)
   )

From 7468aacdbbea9f9b5aed2f6b2cfa85661343c50e Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 19 Aug 2020 08:56:28 -0700
Subject: [PATCH 2/8] fix

---
 src/reason-parser/reason_pprint_ast.ml     | 7 +++----
 src/refmt/reason_implementation_printer.ml | 2 +-
 src/refmt/reason_interface_printer.ml      | 5 +++--
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/reason-parser/reason_pprint_ast.ml b/src/reason-parser/reason_pprint_ast.ml
index 28f77b091..802e5d2e6 100644
--- a/src/reason-parser/reason_pprint_ast.ml
+++ b/src/reason-parser/reason_pprint_ast.ml
@@ -8313,10 +8313,9 @@ let add_explicit_arity_mapper super =
   { super with Ast_mapper. expr; pat }
 
 let preprocessing_mapper =
-  backport_letopt_mapper
-    (ml_to_reason_swap_operator_mapper
-      (escape_stars_slashes_mapper
-        (add_explicit_arity_mapper Ast_mapper.default_mapper)))
+  ml_to_reason_swap_operator_mapper
+    (escape_stars_slashes_mapper
+      (add_explicit_arity_mapper Ast_mapper.default_mapper))
 
 let core_type ppf x =
   format_layout ppf
diff --git a/src/refmt/reason_implementation_printer.ml b/src/refmt/reason_implementation_printer.ml
index b945aa8d4..2c4e93ee9 100644
--- a/src/refmt/reason_implementation_printer.ml
+++ b/src/refmt/reason_implementation_printer.ml
@@ -51,7 +51,7 @@ let print printtype filename parsedAsML output_chan output_formatter =
   )
   | `Binary -> fun (ast, _) ->
     let ast =
-      Reason_syntax_util.(apply_mapper_to_structure ast remove_stylistic_attrs_mapper)
+      Reason_syntax_util.(apply_mapper_to_structure ast (backport_letopt_mapper remove_stylistic_attrs_mapper))
     in
     Ast_io.to_channel output_chan filename
       (Ast_io.Impl ((module OCaml_current),
diff --git a/src/refmt/reason_interface_printer.ml b/src/refmt/reason_interface_printer.ml
index b0a1875ff..b2bb3899d 100644
--- a/src/refmt/reason_interface_printer.ml
+++ b/src/refmt/reason_interface_printer.ml
@@ -49,6 +49,9 @@ let print printtype filename parsedAsML output_chan output_formatter =
     );
   )
   | `Binary -> fun (ast, _) -> (
+      let ast =
+        Reason_syntax_util.(apply_mapper_to_signature ast remove_stylistic_attrs_mapper)
+      in
       Ast_io.to_channel output_chan filename
         (Ast_io.Intf ((module OCaml_current),
                       Reason_toolchain.To_current.copy_signature ast))
@@ -57,8 +60,6 @@ let print printtype filename parsedAsML output_chan output_formatter =
       Printast.interface output_formatter
         (Reason_toolchain.To_current.copy_signature ast)
   )
-  (* If you don't wrap the function in parens, it's a totally different
-   * meaning #thanksOCaml *)
   | `None -> (fun _ -> ())
   | `ML -> Reason_toolchain.ML.print_interface_with_comments output_formatter
   | `Reason -> Reason_toolchain.RE.print_interface_with_comments output_formatter

From be924d552d59551e221134c908bc668d604f45c7 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 19 Aug 2020 09:42:42 -0700
Subject: [PATCH 3/8] fix ocamlmerlin-reason for letop syntax, add
 compatibility with ocaml-syntax-shims

---
 src/reason-merlin/ocamlmerlin_reason.cppo.ml |  6 ++++
 src/reason-parser/reason_syntax_util.cppo.ml | 37 ++++++++++++++++++--
 src/refmt/reason_interface_printer.ml        |  2 +-
 3 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/src/reason-merlin/ocamlmerlin_reason.cppo.ml b/src/reason-merlin/ocamlmerlin_reason.cppo.ml
index a6e8e63ef..89415e289 100644
--- a/src/reason-merlin/ocamlmerlin_reason.cppo.ml
+++ b/src/reason-merlin/ocamlmerlin_reason.cppo.ml
@@ -9,9 +9,15 @@ module Reason_reader = struct
   let load buffer = buffer
 
   let structure str =
+    let str =
+      Reason_syntax_util.(apply_mapper_to_structure str (backport_letopt_mapper remove_stylistic_attrs_mapper))
+    in
     Structure (Reason_toolchain.To_current.copy_structure str)
 
   let signature sg =
+    let sg =
+      Reason_syntax_util.(apply_mapper_to_signature sg (backport_letopt_mapper remove_stylistic_attrs_mapper))
+    in
     Signature (Reason_toolchain.To_current.copy_signature sg)
 
   let parse {text; path} =
diff --git a/src/reason-parser/reason_syntax_util.cppo.ml b/src/reason-parser/reason_syntax_util.cppo.ml
index 8cf869672..91602c517 100644
--- a/src/reason-parser/reason_syntax_util.cppo.ml
+++ b/src/reason-parser/reason_syntax_util.cppo.ml
@@ -594,6 +594,39 @@ let noop_mapper super =
 (* Don't need to backport past 4.08 *)
 let backport_letopt_mapper = noop_mapper
 #else
+  (* Adapted from https://github.com/ocaml-ppx/ocaml-syntax-shims, for
+   * compatibility with OCaml's own backporting. *)
+  let name = function
+    | '!' -> "bang"
+    | '$' -> "dollar"
+    | '%' -> "percent"
+    | '&' -> "ampersand"
+    | '*' -> "star"
+    | '+' -> "plus"
+    | '-' -> "minus"
+    | '/' -> "slash"
+    | ':' -> "colon"
+    | '<' -> "lesser"
+    | '=' -> "equal"
+    | '>' -> "greater"
+    | '?' -> "question"
+    | '@' -> "at"
+    | '^' -> "circumflex"
+    | '|' -> "pipe"
+    | c -> String.make 1 c
+
+  let expand s =
+    let buf = Buffer.create 128 in
+    (* "let" or "and" *)
+    Buffer.add_string buf (String.sub s 0 3);
+    Buffer.add_string buf "__";
+    for i = 3 to String.length s - 1 do
+      if i > 3 then
+        Buffer.add_char buf '_';
+      Buffer.add_string buf (name s.[i])
+    done;
+    Buffer.contents buf
+
 (** This will convert Pexp_letop into a series of `apply`s to simulate 4.08's behavior.
  *
  * For example,
@@ -634,7 +667,7 @@ let backport_letopt_mapper super =
           let (pattern, expr, op) = loop rest in
           let and_op_ident = Ast_helper.Exp.ident
             ~loc:op.loc
-            (Location.mkloc (Longident.Lident op.txt) op.loc)
+            (Location.mkloc (Longident.Lident (expand op.txt)) op.loc)
           in
           (
             Ast_helper.Pat.tuple ~loc:pbop_loc [pbop_pat; pattern],
@@ -645,7 +678,7 @@ let backport_letopt_mapper super =
       let (pattern, expr, _) = loop (let_::ands) in
       let let_op_ident = Ast_helper.Exp.ident
         ~loc:let_.pbop_op.loc
-        (Location.mkloc (Longident.Lident let_.pbop_op.txt) let_.pbop_op.loc)
+        (Location.mkloc (Longident.Lident (expand let_.pbop_op.txt)) let_.pbop_op.loc)
       in
       super.expr mapper {expr with
         pexp_desc = Pexp_apply (let_op_ident,  [
diff --git a/src/refmt/reason_interface_printer.ml b/src/refmt/reason_interface_printer.ml
index b2bb3899d..5a184633e 100644
--- a/src/refmt/reason_interface_printer.ml
+++ b/src/refmt/reason_interface_printer.ml
@@ -50,7 +50,7 @@ let print printtype filename parsedAsML output_chan output_formatter =
   )
   | `Binary -> fun (ast, _) -> (
       let ast =
-        Reason_syntax_util.(apply_mapper_to_signature ast remove_stylistic_attrs_mapper)
+        Reason_syntax_util.(apply_mapper_to_signature ast (backport_letopt_mapper remove_stylistic_attrs_mapper))
       in
       Ast_io.to_channel output_chan filename
         (Ast_io.Intf ((module OCaml_current),

From d02596ae4e9ad9be4f825945b1faaf8ff995ad95 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 19 Aug 2020 10:14:39 -0700
Subject: [PATCH 4/8] expand in the lexer

---
 src/reason-parser/reason_declarative_lexer.mll | 4 ++--
 src/reason-parser/reason_syntax_util.cppo.ml   | 7 ++++---
 src/reason-parser/reason_syntax_util.cppo.mli  | 2 ++
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/reason-parser/reason_declarative_lexer.mll b/src/reason-parser/reason_declarative_lexer.mll
index 9da1f3108..720dacaa1 100644
--- a/src/reason-parser/reason_declarative_lexer.mll
+++ b/src/reason-parser/reason_declarative_lexer.mll
@@ -635,9 +635,9 @@ rule token state = parse
   | '%' operator_chars*
     { INFIXOP3 (lexeme_operator lexbuf) }
   | "let" kwdopchar dotsymbolchar *
-    { LETOP (lexeme_operator lexbuf) }
+    { LETOP (Reason_syntax_util.expand_letop_identifier (lexeme_operator lexbuf)) }
   | "and" kwdopchar dotsymbolchar *
-    { ANDOP (lexeme_operator lexbuf) }
+    { ANDOP (Reason_syntax_util.expand_letop_identifier (lexeme_operator lexbuf)) }
   | eof { EOF }
   | _
     { raise_error
diff --git a/src/reason-parser/reason_syntax_util.cppo.ml b/src/reason-parser/reason_syntax_util.cppo.ml
index 91602c517..62cb71564 100644
--- a/src/reason-parser/reason_syntax_util.cppo.ml
+++ b/src/reason-parser/reason_syntax_util.cppo.ml
@@ -593,6 +593,7 @@ let noop_mapper super =
     signature_item = noop; }
 (* Don't need to backport past 4.08 *)
 let backport_letopt_mapper = noop_mapper
+let expand_letop_identifier s = s
 #else
   (* Adapted from https://github.com/ocaml-ppx/ocaml-syntax-shims, for
    * compatibility with OCaml's own backporting. *)
@@ -615,7 +616,7 @@ let backport_letopt_mapper = noop_mapper
     | '|' -> "pipe"
     | c -> String.make 1 c
 
-  let expand s =
+  let expand_letop_identifier s =
     let buf = Buffer.create 128 in
     (* "let" or "and" *)
     Buffer.add_string buf (String.sub s 0 3);
@@ -667,7 +668,7 @@ let backport_letopt_mapper super =
           let (pattern, expr, op) = loop rest in
           let and_op_ident = Ast_helper.Exp.ident
             ~loc:op.loc
-            (Location.mkloc (Longident.Lident (expand op.txt)) op.loc)
+            (Location.mkloc (Longident.Lident op.txt) op.loc)
           in
           (
             Ast_helper.Pat.tuple ~loc:pbop_loc [pbop_pat; pattern],
@@ -678,7 +679,7 @@ let backport_letopt_mapper super =
       let (pattern, expr, _) = loop (let_::ands) in
       let let_op_ident = Ast_helper.Exp.ident
         ~loc:let_.pbop_op.loc
-        (Location.mkloc (Longident.Lident (expand let_.pbop_op.txt)) let_.pbop_op.loc)
+        (Location.mkloc (Longident.Lident let_.pbop_op.txt) let_.pbop_op.loc)
       in
       super.expr mapper {expr with
         pexp_desc = Pexp_apply (let_op_ident,  [
diff --git a/src/reason-parser/reason_syntax_util.cppo.mli b/src/reason-parser/reason_syntax_util.cppo.mli
index 05f46298a..2b2cbc4cb 100644
--- a/src/reason-parser/reason_syntax_util.cppo.mli
+++ b/src/reason-parser/reason_syntax_util.cppo.mli
@@ -38,6 +38,8 @@ val isLineComment : string -> bool
 
 val remove_stylistic_attrs_mapper : Ast_mapper.mapper
 
+val expand_letop_identifier : string -> string
+
 val backport_letopt_mapper : Ast_mapper.mapper -> Ast_mapper.mapper
 
 val escape_stars_slashes : string -> string

From 88a5b210944d4455d9f1adec3c3b14d9bda949c0 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 19 Aug 2020 10:54:44 -0700
Subject: [PATCH 5/8] print to letop

---
 src/reason-parser/reason_pprint_ast.ml        | 37 +++-----
 src/reason-parser/reason_syntax_util.cppo.ml  | 95 +++++++++++++++----
 src/reason-parser/reason_syntax_util.cppo.mli |  3 +
 3 files changed, 93 insertions(+), 42 deletions(-)

diff --git a/src/reason-parser/reason_pprint_ast.ml b/src/reason-parser/reason_pprint_ast.ml
index 802e5d2e6..78dcdff26 100644
--- a/src/reason-parser/reason_pprint_ast.ml
+++ b/src/reason-parser/reason_pprint_ast.ml
@@ -469,9 +469,6 @@ let unary_plus_prefix_symbols  = ["~+"; "~+." ] ;;
 let infix_symbols = [ '='; '<'; '>'; '@'; '^'; '|'; '&'; '+'; '-'; '*'; '/';
                       '$'; '%'; '\\'; '#' ]
 (* this should match "kwdopchar" from reason_declarative_lexer.mll *)
-let let_monad_symbols = [ '$'; '&'; '*'; '+'; '-'; '/'; '<'; '='; '>'; '@';
-                          '^'; '|'; '.'; '!']
-
 let special_infix_strings =
   ["asr"; "land"; "lor"; "lsl"; "lsr"; "lxor"; "mod"; "or"; ":="; "!="; "!=="]
 
@@ -482,20 +479,6 @@ let requireIndentFor = [updateToken; ":="]
 
 let namedArgSym = "~"
 
-let letop s =
-  String.length s > 3
-  && s.[0] = 'l'
-  && s.[1] = 'e'
-  && s.[2] = 't'
-  && List.mem s.[3] let_monad_symbols
-
-let andop s =
-  String.length s > 3
-  && s.[0] = 'a'
-  && s.[1] = 'n'
-  && s.[2] = 'd'
-  && List.mem s.[3] let_monad_symbols
-
 let requireNoSpaceFor tok =
   tok = pipeFirstToken || (tok.[0] = '#' && tok <> "#=")
 
@@ -531,8 +514,8 @@ let printedStringAndFixity = function
       else
         AlmostSimplePrefix s
   )
-  | s when letop s -> Letop s
-  | s when andop s -> Andop s
+  | s when is_letop s -> Letop s
+  | s when is_andop s -> Andop s
   | _ -> Normal
 
 
@@ -1979,9 +1962,15 @@ let typeApplicationFinalWrapping typeApplicationItems =
 
 (* add parentheses to binders when they are in fact infix or prefix operators *)
 let protectIdentifier txt =
-  if not (needs_parens txt) then atom txt
-  else if needs_spaces txt then makeList ~wrap:("(", ")") ~pad:(true, true) [atom txt]
-  else atom ("(" ^ txt ^ ")")
+  let txt' =
+    if is_andop txt || is_letop txt then
+      Reason_syntax_util.compress_letop_identifier txt
+    else
+      txt
+  in
+  if not (needs_parens txt) then atom txt'
+  else if needs_spaces txt then makeList ~wrap:("(", ")") ~pad:(true, true) [atom txt']
+  else atom ("(" ^ txt' ^ ")")
 
 let protectLongIdentifier longPrefix txt =
   makeList [longPrefix; atom "."; protectIdentifier txt]
@@ -5482,14 +5471,14 @@ let printer = object(self:'self)
         itemsLayout
 
   method letop_bindings { let_; ands } =
-    let label = let_.pbop_op.txt in
+    let label = compress_letop_identifier (let_.pbop_op.txt) in
     let let_item = self#binding_op label let_ in
     match ands with
     | [] -> let_item
     | l ->
       let and_items = List.map (fun x ->
         let loc = extractLocBindingOp x in
-        let layout = self#binding_op x.pbop_op.txt x in
+        let layout = self#binding_op (compress_letop_identifier x.pbop_op.txt) x in
         (loc, layout)
       ) l
       in
diff --git a/src/reason-parser/reason_syntax_util.cppo.ml b/src/reason-parser/reason_syntax_util.cppo.ml
index 62cb71564..1c12c38e9 100644
--- a/src/reason-parser/reason_syntax_util.cppo.ml
+++ b/src/reason-parser/reason_syntax_util.cppo.ml
@@ -582,6 +582,35 @@ let remove_stylistic_attrs_mapper_maker super =
 let remove_stylistic_attrs_mapper =
   remove_stylistic_attrs_mapper_maker Ast_mapper.default_mapper
 
+let let_monad_symbols = [ '$'; '&'; '*'; '+'; '-'; '/'; '<'; '='; '>'; '@';
+                          '^'; '|'; '.'; '!']
+
+let is_letop s =
+  String.length s > 3
+  && s.[0] = 'l'
+  && s.[1] = 'e'
+  && s.[2] = 't'
+#if OCAML_VERSION >= (4, 8, 0)
+  && List.mem s.[3] let_monad_symbols
+#else
+  && s.[3] = '_'
+  && s.[4] = '_'
+  && List.mem s.[5] let_monad_symbols
+#endif
+
+let is_andop s =
+  String.length s > 3
+  && s.[0] = 'a'
+  && s.[1] = 'n'
+  && s.[2] = 'd'
+#if OCAML_VERSION >= (4, 8, 0)
+  && List.mem s.[3] let_monad_symbols
+#else
+  && s.[3] = '_'
+  && s.[4] = '_'
+  && List.mem s.[5] let_monad_symbols
+#endif
+
 #if OCAML_VERSION >= (4, 8, 0)
 let noop_mapper super =
   let noop = fun _mapper x -> x in
@@ -597,24 +626,54 @@ let expand_letop_identifier s = s
 #else
   (* Adapted from https://github.com/ocaml-ppx/ocaml-syntax-shims, for
    * compatibility with OCaml's own backporting. *)
-  let name = function
-    | '!' -> "bang"
-    | '$' -> "dollar"
-    | '%' -> "percent"
-    | '&' -> "ampersand"
-    | '*' -> "star"
-    | '+' -> "plus"
-    | '-' -> "minus"
-    | '/' -> "slash"
-    | ':' -> "colon"
-    | '<' -> "lesser"
-    | '=' -> "equal"
-    | '>' -> "greater"
-    | '?' -> "question"
-    | '@' -> "at"
-    | '^' -> "circumflex"
-    | '|' -> "pipe"
-    | c -> String.make 1 c
+  let letop_table, reverse_letop_table =
+    let create_hashtable n l =
+      let t = Hashtbl.create n in
+      let rev_t = Hashtbl.create n in
+      List.iter (fun (k, v) ->
+        Hashtbl.add t k v;
+      Hashtbl.add rev_t v k;
+      ) l;
+      t, rev_t
+    in
+    create_hashtable 16 [
+      '!', "bang"
+    ; '$', "dollar"
+    ; '%', "percent"
+    ; '&', "ampersand"
+    ; '*', "star"
+    ; '+', "plus"
+    ; '-', "minus"
+    ; '/', "slash"
+    ; ':', "colon"
+    ; '<', "lesser"
+    ; '=', "equal"
+    ; '>', "greater"
+    ; '?', "question"
+    ; '@', "at"
+    ; '^', "circumflex"
+    ; '|', "pipe"
+    ]
+
+  let name s =
+    try Hashtbl.find letop_table s
+    with Not_found -> String.make 1 s
+
+  let rev_name s =
+    try String.make 1 (Hashtbl.find reverse_letop_table s)
+    with Not_found -> s
+
+  let compress_letop_identifier s =
+    let buf = Buffer.create 128 in
+    (* "let" or "and" *)
+    Buffer.add_string buf (String.sub s 0 3);
+    let s = String.sub s 5 (String.length s - 5) in
+    let segments = String.split_on_char '_' s in
+    List.iter (function
+      | "" -> Buffer.add_string buf "_"
+      | segment -> Buffer.add_string buf (rev_name segment))
+      segments;
+    Buffer.contents buf
 
   let expand_letop_identifier s =
     let buf = Buffer.create 128 in
diff --git a/src/reason-parser/reason_syntax_util.cppo.mli b/src/reason-parser/reason_syntax_util.cppo.mli
index 2b2cbc4cb..5f363a9a7 100644
--- a/src/reason-parser/reason_syntax_util.cppo.mli
+++ b/src/reason-parser/reason_syntax_util.cppo.mli
@@ -38,6 +38,9 @@ val isLineComment : string -> bool
 
 val remove_stylistic_attrs_mapper : Ast_mapper.mapper
 
+val is_letop : string -> bool
+val is_andop : string -> bool
+val compress_letop_identifier : string -> string
 val expand_letop_identifier : string -> string
 
 val backport_letopt_mapper : Ast_mapper.mapper -> Ast_mapper.mapper

From a18a94605c09ddfd56144f2a33ea30887188df1b Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 19 Aug 2020 11:07:17 -0700
Subject: [PATCH 6/8] fix test

---
 src/reason-parser/reason_syntax_util.cppo.ml | 38 ++++++++++++--------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/src/reason-parser/reason_syntax_util.cppo.ml b/src/reason-parser/reason_syntax_util.cppo.ml
index 1c12c38e9..d8538e7c6 100644
--- a/src/reason-parser/reason_syntax_util.cppo.ml
+++ b/src/reason-parser/reason_syntax_util.cppo.ml
@@ -579,6 +579,15 @@ let remove_stylistic_attrs_mapper_maker super =
   end;
 }
 
+let escape_stars_slashes str =
+  if String.contains str '/' then
+    replace_string "/*" "/\\*" @@
+    replace_string "*/" "*\\/" @@
+    replace_string "//" "/\\/" @@
+    str
+  else
+    str
+
 let remove_stylistic_attrs_mapper =
   remove_stylistic_attrs_mapper_maker Ast_mapper.default_mapper
 
@@ -586,7 +595,11 @@ let let_monad_symbols = [ '$'; '&'; '*'; '+'; '-'; '/'; '<'; '='; '>'; '@';
                           '^'; '|'; '.'; '!']
 
 let is_letop s =
+#if OCAML_VERSION >= (4, 8, 0)
   String.length s > 3
+#else
+  String.length s > 5
+#endif
   && s.[0] = 'l'
   && s.[1] = 'e'
   && s.[2] = 't'
@@ -599,7 +612,11 @@ let is_letop s =
 #endif
 
 let is_andop s =
+#if OCAML_VERSION >= (4, 8, 0)
   String.length s > 3
+#else
+  String.length s > 5
+#endif
   && s.[0] = 'a'
   && s.[1] = 'n'
   && s.[2] = 'd'
@@ -623,6 +640,7 @@ let noop_mapper super =
 (* Don't need to backport past 4.08 *)
 let backport_letopt_mapper = noop_mapper
 let expand_letop_identifier s = s
+let compress_letop_identifier s = s
 #else
   (* Adapted from https://github.com/ocaml-ppx/ocaml-syntax-shims, for
    * compatibility with OCaml's own backporting. *)
@@ -669,11 +687,12 @@ let expand_letop_identifier s = s
     Buffer.add_string buf (String.sub s 0 3);
     let s = String.sub s 5 (String.length s - 5) in
     let segments = String.split_on_char '_' s in
-    List.iter (function
-      | "" -> Buffer.add_string buf "_"
-      | segment -> Buffer.add_string buf (rev_name segment))
-      segments;
-    Buffer.contents buf
+    let identifier = String.concat "" (List.map (function
+      | "" -> "_"
+      | segment -> rev_name segment) segments)
+    in
+    Buffer.add_string buf identifier;
+    escape_stars_slashes (Buffer.contents buf)
 
   let expand_letop_identifier s =
     let buf = Buffer.create 128 in
@@ -749,15 +768,6 @@ let backport_letopt_mapper super =
 }
 #endif
 
-let escape_stars_slashes str =
-  if String.contains str '/' then
-    replace_string "/*" "/\\*" @@
-    replace_string "*/" "*\\/" @@
-    replace_string "//" "/\\/" @@
-    str
-  else
-    str
-
 (** escape_stars_slashes_mapper escapes all stars and slashes in an AST *)
 let escape_stars_slashes_mapper = identifier_mapper escape_stars_slashes
 

From ef4e819969e46cb144a546e3cc4aa44923db6559 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 19 Aug 2020 11:16:26 -0700
Subject: [PATCH 7/8] one more fix

---
 src/reason-parser/reason_pprint_ast.ml | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/reason-parser/reason_pprint_ast.ml b/src/reason-parser/reason_pprint_ast.ml
index 78dcdff26..5de20f44a 100644
--- a/src/reason-parser/reason_pprint_ast.ml
+++ b/src/reason-parser/reason_pprint_ast.ml
@@ -1962,15 +1962,16 @@ let typeApplicationFinalWrapping typeApplicationItems =
 
 (* add parentheses to binders when they are in fact infix or prefix operators *)
 let protectIdentifier txt =
-  let txt' =
+  let needs_parens = needs_parens txt in
+  let txt =
     if is_andop txt || is_letop txt then
       Reason_syntax_util.compress_letop_identifier txt
     else
       txt
   in
-  if not (needs_parens txt) then atom txt'
-  else if needs_spaces txt then makeList ~wrap:("(", ")") ~pad:(true, true) [atom txt']
-  else atom ("(" ^ txt' ^ ")")
+  if not needs_parens then atom txt
+  else if needs_spaces txt then makeList ~wrap:("(", ")") ~pad:(true, true) [atom txt]
+  else atom ("(" ^ txt ^ ")")
 
 let protectLongIdentifier longPrefix txt =
   makeList [longPrefix; atom "."; protectIdentifier txt]

From 286482590c94e27387c008b4b4a4713da9c53c20 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Wed, 19 Aug 2020 11:21:24 -0700
Subject: [PATCH 8/8] String.split_on_char not available in 4.03

---
 src/reason-parser/reason_syntax_util.cppo.ml | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/reason-parser/reason_syntax_util.cppo.ml b/src/reason-parser/reason_syntax_util.cppo.ml
index d8538e7c6..d7eef8184 100644
--- a/src/reason-parser/reason_syntax_util.cppo.ml
+++ b/src/reason-parser/reason_syntax_util.cppo.ml
@@ -681,12 +681,24 @@ let compress_letop_identifier s = s
     try String.make 1 (Hashtbl.find reverse_letop_table s)
     with Not_found -> s
 
+  let split_on_char sep s =
+    let open String in
+    let r = ref [] in
+    let j = ref (length s) in
+    for i = length s - 1 downto 0 do
+      if unsafe_get s i = sep then begin
+        r := sub s (i + 1) (!j - i - 1) :: !r;
+        j := i
+      end
+    done;
+    sub s 0 !j :: !r
+
   let compress_letop_identifier s =
     let buf = Buffer.create 128 in
     (* "let" or "and" *)
     Buffer.add_string buf (String.sub s 0 3);
     let s = String.sub s 5 (String.length s - 5) in
-    let segments = String.split_on_char '_' s in
+    let segments = split_on_char '_' s in
     let identifier = String.concat "" (List.map (function
       | "" -> "_"
       | segment -> rev_name segment) segments)