From d36c5d1d0dc98a9e5fd1cfadd1981a5b99ff7d8d Mon Sep 17 00:00:00 2001
From: Son Ho
Date: Sat, 29 Jan 2022 21:23:05 +0100
Subject: Start working on StringUtils

---
 src/ExtractToFStar.ml | 17 +++++++++
 src/StringUtils.ml    | 96 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 src/StringUtils.ml

diff --git a/src/ExtractToFStar.ml b/src/ExtractToFStar.ml
index d0726ac7..bb4054c2 100644
--- a/src/ExtractToFStar.ml
+++ b/src/ExtractToFStar.ml
@@ -4,8 +4,25 @@ open Errors
 open Pure
 open TranslateCore
 open PureToExtract
+open StringUtils
 module F = Format
 
+(*
+let mk_name_formatter =
+{
+  bool_name : string;
+  char_name : string;
+  int_name : integer_type -> string;
+  str_name : string;
+  field_name : name -> string option -> string;
+  variant_name : name -> string -> string;
+  type_name : name -> string;
+  fun_name : A.fun_id -> name -> int -> region_group_info option -> string;
+  var_basename : StringSet.t -> ty -> string;
+  type_var_basename : StringSet.t -> string;
+  append_index : string -> int -> string;
+}*)
+
 (** [inside] constrols whether we should add parentheses or not around type
     application (if `true` we add parentheses).
  *)
diff --git a/src/StringUtils.ml b/src/StringUtils.ml
new file mode 100644
index 00000000..6089efc8
--- /dev/null
+++ b/src/StringUtils.ml
@@ -0,0 +1,96 @@
+(** Utilities to work on strings, character per character.
+
+    They operate on ASCII strings, and are used by the project to convert
+    Rust names: Rust names are not fancy, so it shouldn't be a problem.
+    
+    Rk.: the poor support of OCaml for char manipulation is really annoying...
+ *)
+
+let code_0 = 48
+
+let code_9 = 57
+
+let code_A = 65
+
+let code_Z = 90
+
+let code_a = 97
+
+let code_z = 122
+
+let is_lowercase_ascii (c : char) : bool =
+  let c = Char.code c in
+  code_a <= c && c <= code_z
+
+let is_uppercase_ascii (c : char) : bool =
+  let c = Char.code c in
+  code_A <= c && c <= code_Z
+
+let is_letter_ascii (c : char) : bool =
+  is_lowercase_ascii c || is_uppercase_ascii c
+
+let is_digit_ascii (c : char) : bool =
+  let c = Char.code c in
+  code_0 <= c && c <= code_9
+
+let lowercase_ascii = Char.lowercase_ascii
+
+let uppercase_ascii = Char.uppercase_ascii
+
+(** Using buffers as per:
+    [https://stackoverflow.com/questions/29957418/how-to-convert-char-list-to-string-in-ocaml]
+ *)
+let string_of_chars (chars : char list) : string =
+  let buf = Buffer.create (List.length chars) in
+  List.iter (Buffer.add_char buf) chars;
+  Buffer.contents buf
+
+let string_to_chars (s : string) : char list =
+  let length = String.length s in
+  let rec apply i =
+    if i = length then [] else String.get s i :: apply (i + 1)
+  in
+  apply 0
+
+(** This operates on ASCII *)
+let to_camel_case (s : string) : string =
+  (* There are no [fold_left_map] in [String]... *)
+  let mk_upper = ref true in
+  (* TODO: remove '_' *)
+  let apply (c : char) : char =
+    if !mk_upper then (
+      mk_upper := c = '_';
+      uppercase_ascii c)
+    else (
+      mk_upper := c = '_';
+      c)
+  in
+  String.map apply s
+
+(** This operates on ASCII *)
+let to_snake_case (s : string) : string =
+  (* Note that we rebuild the string in invert order *)
+  let apply ((prev_is_low, prev_is_digit, acc) : bool * bool * char list)
+      (c : char) : bool * bool * char list =
+    let acc =
+      if prev_is_digit then if is_letter_ascii c then '_' :: acc else acc
+      else if prev_is_low then
+        if is_lowercase_ascii c || is_digit_ascii c then acc else '_' :: acc
+      else acc
+    in
+    let prev_is_low = is_lowercase_ascii c in
+    let prev_is_digit = is_digit_ascii c in
+    let c = lowercase_ascii c in
+    (prev_is_low, prev_is_digit, c :: acc)
+  in
+  let _, _, chars =
+    List.fold_left apply (false, false, []) (string_to_chars s)
+  in
+  string_of_chars (List.rev chars)
+
+(** Unit tests *)
+let _ =
+  assert (is_digit_ascii '3');
+  assert (is_digit_ascii '6');
+  assert (to_snake_case "HelloWorld36Hello" = "hello_world36_hello");
+  assert (to_snake_case "HELLO" = "hello")
-- 
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