use stag properly, add with_styling.

all tests pass again.

src/core/CCFormat.ml

@@ -312,8 +312,7 @@ module ANSI_codes = struct
 
   exception No_such_style
 
-  (* parse a string tag.
-     TODO: use [stag], for OCaml >= 4.08… *)
+  (* parse a string tag. *)
   let style_of_tag_ s = match String.trim s with
     | "reset" -> [`Reset]
     | "black" -> [`FG `Black]
@@ -343,23 +342,9 @@ let color_enabled = ref false
 
 let mark_open_style st style =
   Stack.push style st;
-  if !color_enabled then string_of_style_list style else ""
+  if !color_enabled then ANSI_codes.string_of_style_list style else ""
 
-let mark_close_style st style =
-
-(* either prints the tag of [s] or delegate to [or_else] *)
-let mark_open_tag st ~or_else s =
-  let open ANSI_codes in
-  try
-    let style = style_of_tag_ s in
-    mark_open_style st style
-  with No_such_style -> or_else s
-
-let mark_close_tag st ~or_else s =
-  let open ANSI_codes in
-  (* check if it's indeed about color *)
-  match style_of_tag_ s with
-    | _ ->
+let mark_close_style st : string =
   let style =
     try
       ignore (Stack.pop st); (* pop current style (if well-scoped …) *)
@@ -367,8 +352,34 @@ let mark_close_tag st ~or_else s =
     with Stack.Empty ->
       [`Reset]
   in
-      if !color_enabled then string_of_style_list style else ""
-    | exception No_such_style -> or_else s
+  if !color_enabled then ANSI_codes.string_of_style_list style else ""
+
+(* either prints the tag of [s] or delegate to [or_else] *)
+let mark_open_tag st ~or_else (tag:stag) : string =
+  match tag with
+  | Style style ->
+    mark_open_style st style;
+  | String_tag s ->
+    let open ANSI_codes in
+    begin
+      try
+        let style = style_of_tag_ s in
+        mark_open_style st style
+      with No_such_style -> or_else tag
+    end
+  | _ -> or_else tag
+
+let mark_close_tag st ~or_else (tag:stag) : string =
+  match tag with
+  | Style _ -> mark_close_style st
+  | String_tag s ->
+    let open ANSI_codes in
+    (* check if it's indeed about color *)
+    begin match style_of_tag_ s with
+      | _ -> mark_close_style st
+      | exception No_such_style -> or_else tag
+    end
+  | _ -> or_else tag
 
 [@@@ifge 4.8]
 
@@ -376,36 +387,33 @@ let mark_close_tag st ~or_else s =
 let pp_open_tag out s = pp_open_stag out (String_tag s)
 let pp_close_tag out () = pp_close_stag out ()
 
-[@@@ocaml.warning "-3"]
-let pp_get_formatter_tag_functions = pp_get_formatter_tag_functions
-let pp_set_formatter_tag_functions = pp_set_formatter_tag_functions
-
-let update_tag_funs_ funs f1 f2 =
+let update_tag_funs_ (funs:formatter_stag_functions) f1 f2 =
   { funs with
-    mark_open_tag = f1 ~or_else:funs.mark_open_tag;
-    mark_close_tag = f2 ~or_else:funs.mark_close_tag;
+    mark_open_stag = f1 ~or_else:funs.mark_open_stag;
+    mark_close_stag = f2 ~or_else:funs.mark_close_stag;
   }
 
-let styling stl pp out x =
+let with_styling stl out f =
   pp_open_stag out (Style stl);
-  try pp out x; pp_close_stag out ()
+  try let x = f() in pp_close_stag out (); x
   with e -> pp_close_stag out (); raise e
 
-[@@@ocaml.warning "+3"]
+let styling stl pp out x =
+  with_styling stl out @@ fun () -> pp out x
 
 [@@@else_]
 
-let update_tag_funs_ funs f1 f2 =
+let update_tag_funs_ (funs:formatter_stag_functions) f1 f2 =
   { funs with
-    mark_open_tag = f1 funs.mark_open_tag;
-    mark_close_tag = f2 funs.mark_close_tag;
+    mark_open_stag = f1 funs.mark_open_stag;
+    mark_close_stag = f2 funs.mark_close_stag;
   }
 
 [@@@endif]
 
 (* add color handling to formatter [ppf] *)
 let set_color_tag_handling ppf =
-  let functions = pp_get_formatter_tag_functions ppf () in
+  let functions = pp_get_formatter_stag_functions ppf () in
   let st = Stack.create () in (* stack of styles *)
   let functions' =
     update_tag_funs_ functions
@@ -413,7 +421,7 @@ let set_color_tag_handling ppf =
       (mark_close_tag st)
   in
   pp_set_mark_tags ppf true; (* enable tags *)
-  pp_set_formatter_tag_functions ppf functions'
+  pp_set_formatter_stag_functions ppf functions'
 
 let set_color_default =
   let first = ref true in
@@ -437,6 +445,19 @@ let set_color_default =
     s
 *)
 
+(*$R
+  set_color_default true;
+  let s = sprintf
+    "what is your %a? %a! No, %a! Ahhhhhhh@."
+    (styling [`FG `White; `Bold] string) "favorite color"
+    (styling [`FG `Blue] string) "blue"
+    (styling [`FG `Red] string) "red"
+  in
+  assert_equal ~printer:CCFun.id
+    "what is your \027[37;1mfavorite color\027[0m? \027[34mblue\027[0m! No, \027[31mred\027[0m! Ahhhhhhh\n"
+    s
+*)
+
 let with_color s pp out x =
   pp_open_tag out s;
   pp out x;

src/core/CCFormat.mli

@@ -330,6 +330,26 @@ val styling : ANSI_codes.style list -> 'a printer -> 'a printer
 (** [styling st p] is the same printer as [p], except it locally sets
     the style [st].
 
+    Example:
+    {[
+
+    open CCFormat;
+    set_color_default true;
+    sprintf
+      "what is your %a? %a! No, %a! Ahhhhhhh@."
+      (styling [`FG `White; `Bold] string) "favorite color"
+      (styling [`FG `Blue] string) "blue"
+      (styling [`FG `Red] string) "red"
+    ]}
+
+    Available only on OCaml >= 4.08.
+    @since NEXT_RELEASE *)
+
+val with_styling : ANSI_codes.style list -> t -> (unit -> 'a) -> 'a
+(** [with_styling style fmt f] sets the given style on [fmt],
+    calls [f()], then restores the previous style.
+    It is useful in imperative-style printers (a sequence of "print a; print b; …").
+
     Available only on OCaml >= 4.08.
     @since NEXT_RELEASE *)