Re: [Caml-list] [batteries] ... how to create (format) directives that do not take any arguments?

[Gabriel Scherer <gabriel.scherer@gmail.com>]

Adding custom printing directives requires a syntax extension to
rewrite those directives into OCaml code. The built-in support for
magicly-typed formats in the OCaml language is not extensible (it is
complex enough as it is).
Batteries 1 used to provide such a syntax extension, but we
(re)discovered that users don't like syntax extensions: they make code
harder to compile/deploy, are controversial, and in the long run often
make our life harder instead of easier. Batteries 2 does not come with
any syntax extension, and I think we're better off as is (of course
you're free to add your own in your code).

Of course, such a natural idea is bound to be reused, and one of the
first libraries released by Jérémie Dimino at Jane Street was
precisely such a custom-printf camlp4 extension:
  https://github.com/janestreet/custom_printf

Feel free to reuse it or extend it for any project where it makes
sense. In particular, I don't think that using it implies any
dependency of your preprocessed code on Core, though of course you'll
need Sexplib to use the format-to-sexplib feature. My purely personal
advice would be to seriously explore non-syntax-extension approaches
(combinator library?) before making such a step.

On Mon, Nov 25, 2013 at 4:46 PM, Matej Kosik
<5764c029b688c1c0d24a2e97cd764f@gmail.com> wrote:
> Dear all,
>
> I would like to define custom directives, that would enable me to write code like e.g. this:
>
> Print.printf "regular %bold_on bold %bold_off regular %italic_on italic %italic_off";
>
> This might expand to (in HTML codes)
>
>               regular <B>bold</B> regular <I>italic</I>
>
> or in ANSI codes to something analogous.
>
> I am currently looking at:
>
>   http://ocaml-batteries-team.github.io/batteries-included/hdoc/BatPrint.html
>
> It refers to:
>
>   https://github.com/ocaml-batteries-team/batteries-included/blob/master/examples/snippets/test_printf.ml
>
> Those things work, although there is no example for:
>
>   Print.literal
>
> which might be (?) what I need to employ.
>
> Can somebody give me some advice how to create simple "parameterless format directives" (like those above)?
>
> ----
>
> Basically, I just want to refactor some weird markup out of the literal string while I do not want to reinsert the refactored stuff via %s because it is not maintainable.
>
> --
> Caml-list mailing list.  Subscription management and archives:
> https://sympa.inria.fr/sympa/arc/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs