[Caml-list] Format questions

[Caml-list] Format questions

[Matej Kosik]

Hi everybody,

I am trying to understand the concepts in the Format module.

While reading this:

  https://ocaml.org/learn/tutorials/format.html

One of the mini experiments I did was:

  set_margin 11;
  open_hvbox 0;
  print_string "---";
  print_space ();
  print_string "---";
  print_space ();
  print_string "---";
  print_newline ();
  print_newline ();

I've got the expected output, which is:

  ---
  ---
  ---

No surprises.

However, when I tried to write express the same intentions via Format.fprintf function:

  Format.set_margin 11;
  Format.fprintf std_formatter "@[<hv 0>---@ ---@ ---@.@.";

I get:

  --- --- ---

I'd like to ask for some clues as to why the output of the above Format.fprintf is different from the more verbose version above.

(this is the one module that, to this day, seems a bit mysterious to me --- that is why I ask)

Thanks in advance for the help.

Re: [Caml-list] Format questions

[Josh Berdine]

On Sat, Apr 08 2017, Matej Kosik wrote:

> Hi everybody,
>
> I am trying to understand the concepts in the Format module.
>
> While reading this:
>
>   https://ocaml.org/learn/tutorials/format.html
>
> One of the mini experiments I did was:
>
>   set_margin 11;
>   open_hvbox 0;
>   print_string "---";
>   print_space ();
>   print_string "---";
>   print_space ();
>   print_string "---";
>   print_newline ();
>   print_newline ();
>
> I've got the expected output, which is:
>
>   ---
>   ---
>   ---
>
> No surprises.
>
> However, when I tried to write express the same intentions via Format.fprintf function:
>
>   Format.set_margin 11;
>   Format.fprintf std_formatter "@[<hv 0>---@ ---@ ---@.@.";
>
> I get:
>
>   --- --- ---
>
> I'd like to ask for some clues as to why the output of the above Format.fprintf is different from the more verbose version above.

Are you, by chance, evaluating this in utop (which seems to mess with std_formatter)?   I see your expected behavior using the standard toplevel.  (After adding Format. to std_formatter)

Re: [Caml-list] Format questions

[Matej Kosik]

Hi Josh,

On 04/09/2017 12:24 AM, Josh Berdine wrote:
> On Sat, Apr 08 2017, Matej Kosik wrote:
> 
>> Hi everybody,
>>
>> I am trying to understand the concepts in the Format module.
>>
>> While reading this:
>>
>>   https://ocaml.org/learn/tutorials/format.html
>>
>> One of the mini experiments I did was:
>>
>>   set_margin 11;
>>   open_hvbox 0;
>>   print_string "---";
>>   print_space ();
>>   print_string "---";
>>   print_space ();
>>   print_string "---";
>>   print_newline ();
>>   print_newline ();
>>
>> I've got the expected output, which is:
>>
>>   ---
>>   ---
>>   ---
>>
>> No surprises.
>>
>> However, when I tried to write express the same intentions via Format.fprintf function:
>>
>>   Format.set_margin 11;
>>   Format.fprintf std_formatter "@[<hv 0>---@ ---@ ---@.@.";
>>
>> I get:
>>
>>   --- --- ---
>>
>> I'd like to ask for some clues as to why the output of the above Format.fprintf is different from the more verbose version above.
> 
> Are you, by chance, evaluating this in utop (which seems to mess with std_formatter)?   I see your expected behavior using the standard toplevel.  (After adding Format. to std_formatter)

I was using standard Ocaml toplevel
(in a context where I opened Format module).

I looked at it today and I have realized that instead of this:

  set_margin 11;

if I want to use "Format.fprintf std_formatter" I should do

  pp_set_margin std_formatter 11;

as if

  set_margin <> pp_set_margin std_formatter

That I did not know.

Re: [Caml-list] Format questions

[Nicolás Ojeda Bär]

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Hi Matej,

I do not think that is the reason, as both calls do the same thing, see

  https://github.com/ocaml/ocaml/blob/trunk/stdlib/format.ml#L1153

Cheers,
Nicolas


On Sun, Apr 9, 2017 at 9:44 AM, Matej Kosik <
5764c029b688c1c0d24a2e97cd764f@gmail.com> wrote:

> Hi Josh,
>
> On 04/09/2017 12:24 AM, Josh Berdine wrote:
> > On Sat, Apr 08 2017, Matej Kosik wrote:
> >
> >> Hi everybody,
> >>
> >> I am trying to understand the concepts in the Format module.
> >>
> >> While reading this:
> >>
> >>   https://ocaml.org/learn/tutorials/format.html
> >>
> >> One of the mini experiments I did was:
> >>
> >>   set_margin 11;
> >>   open_hvbox 0;
> >>   print_string "---";
> >>   print_space ();
> >>   print_string "---";
> >>   print_space ();
> >>   print_string "---";
> >>   print_newline ();
> >>   print_newline ();
> >>
> >> I've got the expected output, which is:
> >>
> >>   ---
> >>   ---
> >>   ---
> >>
> >> No surprises.
> >>
> >> However, when I tried to write express the same intentions via
> Format.fprintf function:
> >>
> >>   Format.set_margin 11;
> >>   Format.fprintf std_formatter "@[<hv 0>---@ ---@ ---@.@.";
> >>
> >> I get:
> >>
> >>   --- --- ---
> >>
> >> I'd like to ask for some clues as to why the output of the above
> Format.fprintf is different from the more verbose version above.
> >
> > Are you, by chance, evaluating this in utop (which seems to mess with
> std_formatter)?   I see your expected behavior using the standard
> toplevel.  (After adding Format. to std_formatter)
>
> I was using standard Ocaml toplevel
> (in a context where I opened Format module).
>
> I looked at it today and I have realized that instead of this:
>
>   set_margin 11;
>
> if I want to use "Format.fprintf std_formatter" I should do
>
>   pp_set_margin std_formatter 11;
>
> as if
>
>   set_margin <> pp_set_margin std_formatter
>
> That I did not know.
>
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