Re: [Caml-list] A question about Format and semantic tags

[Benoit Vaugon <benoit.vaugon@gmail.com>]

Hello Alan,

In fact, the Format tag activation is local to a formatter. The function 
Format.set_tags enables tags only for the std_formatter (associated to 
stdout). If you want to activate tags for the Format.str_formatter, you 
should call:

Format.pp_set_tags Format.str_formatter true;

instead of:

Format.set_tags true;
Format.set_mark_tags true;

Benoît.


Le 23/03/2016 13:47, Alan Schmitt a écrit :
> Hello,
>
> I need to output two versions of a string that only differ by the
> presence of some markers in them, and I want the output to be pretty
> (it's code to be read). It seems that semantic tags from the Format
> module would allow me to do this, with identical line breaking as these
> tags are considered 0 width. Unfortunately I cannot seem to make it
> work. Here is what I have tried:
>
> #+begin_src ocaml
> let file_put_contents filename text =
>     try
>        let handle = open_out filename in
>        output_string handle text;
>        close_out handle
>     with Sys_error s ->
>       failwith ("Could not write in file: " ^ filename ^ "\n" ^ s)
>
> let filename = "test_out.txt"
>
> let out = "@[<hov 2>Hello World@ Hello@ Hello again@ Hello@ Hello again@ Hello@ Hello again@ @{<foo>Hello@ Cut again@}@]"
>
> let _ =
>    Format.set_tags true;
>    Format.set_mark_tags true;
>    Format.fprintf Format.str_formatter (Scanf.format_from_string out "");
>    file_put_contents filename (Format.flush_str_formatter ())
> #+end_src
>
> To run this I do ~ocamlc -o tags tags.ml && ./tags && cat test_out.txt~.
>
> As I have turned on treatment of tags and tag marking, I would expect to
> see the tag marker in the output string using the default format (<foo>
> and </foo>), but I do not see them.
>
> Am I on the right track by using tags? Could someone point me to my
> mistake?
>
> Thanks a lot,
>
> Alan
>