Re: [Caml-list] Vagaries of Printf variants

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

If you know from the start that you need this flexibility, the easiest
way is probably to use Printf.bprintf from the start, which is
reasonably efficient and flexible (or write your fprintf-formats with
%s rather than %a).

If you specifically need to convert code that uses (f)printf with
minimal changes, you have the problem that your %a/%t functions work
with out_channel, not strings. The simplest way out is probably to use
Unix.pipe (which is available on Windows) to create an out_channel
that you write into and read back the content as a string.

On Tue, Oct 28, 2014 at 10:04 AM, David Allsopp <dra-news@metastack.com> wrote:
> Daniel Bünzli wrote:
>> Le lundi, 27 octobre 2014 à 18:56, David Allsopp a écrit :
>> > but I'm sure there's a reason for its being that way!
>>
>> You may be interested in reading this:
>>
>> http://gallium.inria.fr/blog/format6/
>
> Thanks, that is enlightening! I guess the thing that gets "in the way" is the design decision to make %a operate on the printf-behaviour (i.e. for fprintf, it writes to a channel, for bprintf it writes to a buffer) rather than making %a and %t *always* return a string.
>
>> P.S. If you are using formatters the problem is less acute. Nowadays you
>> can simply define formatters for each of your types with:
>>
>> pp : Format.formatter -> t -> unit
>>
>> and a to_string function is one `Format.asprintf "%a" pp` away.
>
> I was abusing terminology - by formatters I meant printf functions i.e. selecting between ikfprintf, kfprintf, etc. in the same functions.
>
> I haven't looked at the 4.02 sources, but for what I'm doing in 4.01, what would actually be useful would be if Printf.mkprintf were public so that I could supply an alternate function for output_string (i.e. allow Printf.printf to proceed entirely as normal but do something ever-so-slightly different with the final result - and with a different format6 from using ksprintf).
>
>
> David
>
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