feat(CCString): add CCString.uniq

CCString.uniq remove consecutive duplicate characters

src/core/CCString.ml

@@ -1000,6 +1000,24 @@ let filter f s =
   Q.printable_string (fun s -> filter (fun _ -> true) s = s)
 *)
 
+let uniq eq s =
+  if String.length s = 0 then s
+  else begin
+    let buf = Buffer.create (String.length s) in
+    Buffer.add_char buf s.[0];
+    let _ = fold
+        (fun previous_c c ->
+           if not (eq previous_c c) then Buffer.add_char buf c;
+           c
+        )
+        s.[0] s in
+    Buffer.contents buf
+  end
+
+(*$= & ~printer:Q.Print.string
+  "abcde" (uniq CCShims_.Stdlib.(=) "abbccdeeeee")
+*)
+
 let flat_map ?sep f s =
   let buf = Buffer.create (String.length s) in
   iteri

src/core/CCString.mli

@@ -249,6 +249,10 @@ val filter : (char -> bool) -> string -> string
 (** [filter f s] discards characters of [s] not satisfying [f].
     @since 0.17 *)
 
+val uniq : (char -> char -> bool) -> string -> string
+(** [uniq eq s] remove consecutive duplicate characters in [s].
+    @since NEXT_RELEASE *)
+
 val flat_map : ?sep:string -> (char -> string) -> string -> string
 (** [flat_map ~sep f s] maps each chars of [s] to a string, then concatenates them all.
     @param sep optional separator between each generated string.

src/core/CCStringLabels.mli

@@ -254,6 +254,10 @@ val filter : f:(char -> bool) -> string -> string
 (** [filter ~f s] discards characters of [s] not satisfying [f].
     @since 0.17 *)
 
+val uniq : eq:(char -> char -> bool) -> string -> string
+(** [uniq ~eq s] remove consecutive duplicate characters in [s].
+    @since NEXT_RELEASE *)
+
 val flat_map : ?sep:string -> f:(char -> string) -> string -> string
 (** [flat_map ?sep ~f s] maps each chars of [s] to a string, then concatenates them all.
     @param sep optional separator between each generated string.