Re: [PROPOSAL] with_cur_ios() function in the stdlib

[Jose E. Marchesi]

> On Sun, Apr 10, 2022 at 02:22:13PM +0430, Mohammad-Reza Nabipoor wrote:
>> Hello.
>> 
>> On Sat, Apr 09, 2022 at 07:55:16PM +0200, apache2 wrote:
>> > type void_lambda = ()void;
>> > fun with_cur_ios = (string filename, void_lambda callback)void:
>> >   {
>> >...
>> >   }
>> 
>> 
>> What about changing the function paramater `callback` to `do`, and change the
>> `filename` to `handle`, then user can use:
>> 
>> ```poke
>> with_cur_ios
>>   :handle "Hi"
>>   :do lambda void:
>>       {
>>       };
>> 
>> ```

This is a really nice way to use named argument calls :)

It also fixes the problem of passing flags, etc, since with all
arguments getting default values, we can omit all/only some of them, and
call them in any order.

You know what, using this style we can actually just live with one
function, by having a default value for `handler' to the
`get_temp_handler' function that mohammad wrote, which would generate an
unique name for a memory IOS.

Then we can simply do:

with_cur_ios
  :do lambda void: {
       ...
      }

And it will use a temporary MEM IOS with an unique (and not really
interesting to the user) name.

Very nice :)

>
> I like this a lot! I wasn't aware of the named arguments syntax.
>
> I revised the patch and tried to write documentation for it :-)
>
>>From 9043cf8adea070fa2c714e7295389d908101d912 Mon Sep 17 00:00:00 2001
> From: apache2 <apache2+poke-devel@ageinghacker.net>
> Date: Sun, 10 Apr 2022 12:15:40 +0200
> Subject: [PATCH] with_cur_ios function
>
> ---
>  doc/poke.texi     | 35 +++++++++++++++++++++++++++++++++++
>  libpoke/pkl-rt.pk | 21 +++++++++++++++++++++
>  2 files changed, 56 insertions(+)
>
> diff --git a/doc/poke.texi b/doc/poke.texi
> index 2c8201e0..8a315307 100644
> --- a/doc/poke.texi
> +++ b/doc/poke.texi
> @@ -12644,6 +12644,7 @@ memory of some process.
>  * get_ios::                  Getting the current IO space.
>  * set_ios::                  Setting the current IO space.
>  * openset::                     Opening and setting combined.
> +* with_cur_ios::                Exception-safe IO wrapper.
>  * iosize::                   Getting the size of an IO space.
>  * iohandler::                   Getting the handler string of an IO space.
>  * ioflags::                     Getting the flags of an IO space.
> @@ -12859,6 +12860,40 @@ fun openset = (string @var{handler}, uint<64> 
> @var{flags} = 0) int<32>
>  Where the meaning of @var{handler}, @var{flags} and the returned value
>  are exactly like in @code{open}.
>  
> +@node with_cur_ios
> +@subsubsection @code{with_cur_ios}
> +@cindex @code{with_cur_ios}
> +
> +@example
> +fun with_cur_ios = (string @var{handle}, With_Ios_Fn do = lambda void:{}, 
> uint<64> flags = 0) void
> +@end example
> +
> +The @code{with_cur_ios} utility function opens a IO space, like 
> @code{openset},
> +but takes care of calling @code{close} and restoring the original current IO 
> space
> +after the lambda returns or raises an exception.
> +
> +It can be used to deal with files without risk of leaking file descriptors.
> +
> +@example
> +with_cur_ios("*buf*", lambda void:
> +  @{
> +    var arr = uint<32>[1] @ 0#B;
> +    arr[0] = 0x1234;
> +    printf("%v", byte[4] @ 0#b);
> +  @});
> +[0x00UB,0x00UB,0x12UB,0x34UB]
> +
> +with_cur_ios
> +  :handle "*buf*"
> +  :flags IOS_F_CREATE
> +  :do lambda void:
> +  @{
> +    var arr = uint<32>[1] @ 0#B;
> +    arr[0] = 0x1234;
> +    printf("%v", byte[4] @ 0#b);
> +  @}
> +@end example
> +
>  @node iosize
>  @subsubsection @code{iosize}
>  @cindex @code{iosize}
> diff --git a/libpoke/pkl-rt.pk b/libpoke/pkl-rt.pk
> index c6b3209c..03d39970 100644
> --- a/libpoke/pkl-rt.pk
> +++ b/libpoke/pkl-rt.pk
> @@ -563,6 +563,27 @@ immutable fun _pkl_run_ios_set_hook = (int<32> ios) void:
>      f (ios);
>  }
>  
> +immutable type With_Ios_Fn = () void;

I would prefix this type with _pkl, since it is not really expected to
be referred explicitly by users.

> +immutable fun with_cur_ios = (string handle, With_Ios_Fn do = lambda 
> void:{}, uint<32> flags = 0) void:

Please split the line, it is too long.


> +{
> +  var old_ios = get_ios ?! E_no_ios ? get_ios : -1;
> +  var new_ios = open(handle, flags);

In function calls, please leave a space between the name of the function
and the arguments list.

> +  set_ios(new_ios);

Likewise.

> +  try
> +  {
> +    do();

Likewise.

> +    close(new_ios);

Likewise.

> +    if (-1 != old_ios) set_ios(old_ios);
> +  }
> +  catch (Exception exc)
> +  {
> +    close(new_ios);

Likewise.

> +    if (-1 != old_ios) set_ios(old_ios);

Likewise.

> +    raise exc;
> +  }
> +}
> +
>  /**** Set the default load path ****/
>  
>  immutable var load_path = "";