[Caml-list] type-safe printf

[Caml-list] type-safe printf

[Андрей Бергман]

Hello,

is there a good article or just short explanation how compile-type checking of Printf arguments works?

Does it require special compiler support like in C++ compilers/analyzers, or one can somehow do the trick of parsing string literal using Ocaml language itself? (actually latter does not look possible to me)

Thanks,
    Andrey.

Re: [Caml-list] type-safe printf

[Mario Pereira]

Hi,

You can do it using GADTs. However, I am not sure if this is explained 
somewhere.

Le 13/09/2016 à 17:12, Андрей Бергман a écrit :
> Hello,
>
> is there a good article or just short explanation how compile-type checking of Printf arguments works?
>
> Does it require special compiler support like in C++ compilers/analyzers, or one can somehow do the trick of parsing string literal using Ocaml language itself? (actually latter does not look possible to me)
>
> Thanks,
>      Andrey.
>

Re: [Caml-list] type-safe printf

[Kakadu]

Functional unparsing by Olivier Danvy can be related article.
http://www.brics.dk/RS/98/12/BRICS-RS-98-12.pdf


Happy hacking,
Kakadu

On Tue, Sep 13, 2016 at 6:12 PM, Андрей Бергман <vkni@yandex.ru> wrote:
> Hello,
>
> is there a good article or just short explanation how compile-type checking of Printf arguments works?
>
> Does it require special compiler support like in C++ compilers/analyzers, or one can somehow do the trick of parsing string literal using Ocaml language itself? (actually latter does not look possible to me)
>
> Thanks,
>     Andrey.
>
> --
> 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

Re: [Caml-list] type-safe printf

[Maxime Dénès]

Hello,

Some ideas are described here:

https://ocaml.org/meetings/ocaml/2013/proposals/formats-as-gadts.pdf

Maxime.

On 09/13/16 17:25, Mario Pereira wrote:
> Hi,
> 
> You can do it using GADTs. However, I am not sure if this is explained
> somewhere.
> 
> Le 13/09/2016 à 17:12, Андрей Бергман a écrit :
>> Hello,
>>
>> is there a good article or just short explanation how compile-type
>> checking of Printf arguments works?
>>
>> Does it require special compiler support like in C++
>> compilers/analyzers, or one can somehow do the trick of parsing string
>> literal using Ocaml language itself? (actually latter does not look
>> possible to me)
>>
>> Thanks,
>>      Andrey.
>>
> 
> 

RE: [Caml-list] type-safe printf

[David Allsopp]

Андрей Бергман wrote: 
> is there a good article or just short explanation how compile-type
> checking of Printf arguments works?
>
>
> Does it require special compiler support like in C++ compilers/analyzers,
> or one can somehow do the trick of parsing string literal using Ocaml
> language itself? (actually latter does not look possible to me)

It does require a certain amount of special support, yes - see the Pexp_constant(Pconst_string _) case in typing/typecore.ml, in particular the comment "Terrible hack for format strings"! In essence, a string is "magically" interpreted as a format string if it is used in a context where one would be expected (e.g. the usual Printf.printf). It's one of the reasons Pervasives.format_of_string exists (because they're type- rather than syntax-driven).

From that point onwards, it's a lot of GADTs, but doesn't require any special language support!

If you were adding Printf to OCaml for the first time now, you'd probably use quoted string literals instead (see http://caml.inria.fr/pub/docs/manual-ocaml/extn.html#sec249) - and the entire thing would then be in OCaml with no special case hacks.


David

Re: [Caml-list] type-safe printf

[Daniel Bünzli]

On Tuesday 13 September 2016 at 17:31, Kakadu wrote:
> Functional unparsing by Olivier Danvy can be related article.
> http://www.brics.dk/RS/98/12/BRICS-RS-98-12.pdf

That's a good reference. You may also want to have a look at Gabriel Radanne's recent blog post here:

http://drup.github.io/2016/08/02/difflists/

which will show you how to do the same with GADTs, which is a bit more convenient. 

Best, 

Daniel

Re: [Caml-list] type-safe printf

[Андрей Бергман]

Thank you all very much! Your references and explanations made it clear to me.

13.09.2016, 18:19, "Андрей Бергман" <vkni@yandex.ru>:
> Hello,
>
> is there a good article or just short explanation how compile-type checking of Printf arguments works?
>
> Does it require special compiler support like in C++ compilers/analyzers, or one can somehow do the trick of parsing string literal using Ocaml language itself? (actually latter does not look possible to me)
>
> Thanks,
>     Andrey.
>
> --
> 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

Re: [Caml-list] type-safe printf

[Oleg]

> Functional unparsing by Olivier Danvy can be related article.
> http://www.brics.dk/RS/98/12/BRICS-RS-98-12.pdf

Well, in that vein one can point out

        Functional un|unparsing
        http://okmij.org/ftp/typed-formatting/index.html#derivation

which deals with both type-safe printf and scanf (and, moreover, using
exactly the same format for both printing and parsing) and derives even
more type-safe parsing/unparsing methods.