Text_IO from a stream

Text_IO from a stream

[gautier_niouzes]

...is it possible ?
The RM tells about the reverse, getting a stream access from a text
file (Text_IO.Text_Streams).
TIA
______________________________________________________________
Gautier         -- http://www.mysunrise.ch/users/gdm/index.htm
Ada programming -- http://www.mysunrise.ch/users/gdm/gsoft.htm

NB: For a direct answer, e-mail address on the Web site!

Re: Text_IO from a stream

[Dmitry A. Kazakov]

On Mon, 31 Mar 2008 08:27:21 -0700 (PDT), gautier_niouzes@hotmail.com
wrote:

> ...is it possible ?
> The RM tells about the reverse, getting a stream access from a text
> file (Text_IO.Text_Streams).

You can always wrap a File_Type in your own stream object.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: Text_IO from a stream

[gautier_niouzes]

Dmitry A. Kazakov:

> You can always wrap a File_Type in your own stream object.

Do you mean something like:

 type Text_Stream_Type is new Ada.Streams.Root_Stream_Type with record
   virtual_file : Ada.Text_IO.File_Type;
 end record;

?
At the end of the day, what I'd really like is
  function File(stream: access Ada.Streams.Root_Stream_Type 'Class)
return Ada.Text_IO.File_Type;
so that I can do read ASCII data from any stream:
  f:= File(my_stream);
  -- f is as if open in In_File mode
  Get_Line(f, a_string, length);
  Get(f, an_integer); -- not binary, but 123_456
  Get(f, a_float);    -- not binary, but -123.456e78

I guess it would be difficult... But maybe I'm wrong ?
Gautier

Re: Text_IO from a stream

[Dmitry A. Kazakov]

On Mon, 31 Mar 2008 09:05:35 -0700 (PDT), gautier_niouzes@hotmail.com
wrote:

> Dmitry A. Kazakov:
> 
>> You can always wrap a File_Type in your own stream object.
> 
> Do you mean something like:
> 
>  type Text_Stream_Type is new Ada.Streams.Root_Stream_Type with record
>    virtual_file : Ada.Text_IO.File_Type;
>  end record;

Yes

> At the end of the day, what I'd really like is
>   function File(stream: access Ada.Streams.Root_Stream_Type 'Class)
> return Ada.Text_IO.File_Type;
> so that I can do read ASCII data from any stream:
>   f:= File(my_stream);
>   -- f is as if open in In_File mode
>   Get_Line(f, a_string, length);
>   Get(f, an_integer); -- not binary, but 123_456
>   Get(f, a_float);    -- not binary, but -123.456e78
> 
> I guess it would be difficult... But maybe I'm wrong ?
> Gautier

But a stream has no defined formatting and is unrelated to ASCII. Then the
idea of parsing stream looks problematic. If you have in the stream a
sequence "  +  -", what Get should do after discovering '-'?

Anyway, it is quite simple to do. You can do

   type Formatted_Stream (Source : access Root_Stream_Type'Class) is
      tagged limited private;
   function Get (Stream : access Formatted_Stream) return Integer;
   ...

The implementation of Formatted_Stream will use Source for all its I/O. So
you could hang it on any existing stream.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: Text_IO from a stream

[Gautier]

Dmitry A. Kazakov:
> But a stream has no defined formatting and is unrelated to ASCII.

Still, you can read the stream through Character'Read(s,c).

 > Then the idea of parsing stream looks problematic. If you have in the stream a
> sequence "  +  -", what Get should do after discovering '-'?

Exactly the same behaviour as when parsing an ill-formatted text.
Reading a text file (or supposedly so) indirectly via a stream and Stream_IO 
would have the same result that via Ada.Text_IO.

> Anyway, it is quite simple to do. You can do
> 
>    type Formatted_Stream (Source : access Root_Stream_Type'Class) is
>       tagged limited private;
>    function Get (Stream : access Formatted_Stream) return Integer;
>    ...
> 
> The implementation of Formatted_Stream will use Source for all its I/O. So
> you could hang it on any existing stream.

Fine, seems I need to rewrite a Text_IO for streams. I hoped for a ready-made 
solution...
Well, I think I'll switch to a binary format...
______________________________________________________________
Gautier         -- http://www.mysunrise.ch/users/gdm/index.htm
Ada programming -- http://www.mysunrise.ch/users/gdm/gsoft.htm

NB: For a direct answer, e-mail address on the Web site!

Re: Text_IO from a stream

[Dmitry A. Kazakov]

On Mon, 31 Mar 2008 21:17:10 +0200, Gautier wrote:

> Dmitry A. Kazakov:
>> But a stream has no defined formatting and is unrelated to ASCII.
> 
> Still, you can read the stream through Character'Read(s,c).

Yes, but will that be ASCII-encoded? And it has somehow invent lines and
pages.

>> Then the idea of parsing stream looks problematic. If you have in the stream a
>> sequence "  +  -", what Get should do after discovering '-'?
> 
> Exactly the same behaviour as when parsing an ill-formatted text.

Ah, yes. I cannot find the place in ARM, but it seems that Text_IO would
swallow syntactically incorrect input before propagating Data_Error.

> Reading a text file (or supposedly so) indirectly via a stream and Stream_IO 
> would have the same result that via Ada.Text_IO.
> 
>> Anyway, it is quite simple to do. You can do
>> 
>>    type Formatted_Stream (Source : access Root_Stream_Type'Class) is
>>       tagged limited private;
>>    function Get (Stream : access Formatted_Stream) return Integer;
>>    ...
>> 
>> The implementation of Formatted_Stream will use Source for all its I/O. So
>> you could hang it on any existing stream.
> 
> Fine, seems I need to rewrite a Text_IO for streams. I hoped for a ready-made 
> solution...

But Text_IO also defines all Get procedures on String. So if you knew where
line ends are in your stream you could cache the current line in
Formatted_Stream and then simply route all its Gets to Ada.Text_IO Gets.

> Well, I think I'll switch to a binary format...

I would do that too. Also I would override 'Read and 'Write in order to
make it platform-independent. (Stream_Element should be replaced by
octets.)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: Text_IO from a stream

[Gautier]

Dmitry A. Kazakov:

> Yes, but will that be ASCII-encoded? And it has somehow invent lines and
> pages.

Sure, it is indeed a zip-archived text file that I intend to read through 
UnZip.Streams.

Meanwhile (#ada irc...) there seems to be a nice solution:

http://jesselang.com/software/streams_text_io/

...
>> Well, I think I'll switch to a binary format...
> 
> I would do that too. Also I would override 'Read and 'Write in order to
> make it platform-independent. (Stream_Element should be replaced by
> octets.)

No problem with that - there is already a framework in that package (for other 
files) that sends things byte-per-byte in a deterministic endianess; floats are 
split/merged with certain a Float_portable_binary_transfer package.

Thanks for the help!
______________________________________________________________
Gautier         -- http://www.mysunrise.ch/users/gdm/index.htm
Ada programming -- http://www.mysunrise.ch/users/gdm/gsoft.htm

NB: For a direct answer, e-mail address on the Web site!

Re: Text_IO from a stream

[Dmitry A. Kazakov]

On Mon, 31 Mar 2008 22:54:35 +0200, Gautier wrote:

> Dmitry A. Kazakov:
> 
> Meanwhile (#ada irc...) there seems to be a nice solution:
> 
> http://jesselang.com/software/streams_text_io/

Yes.

>>> Well, I think I'll switch to a binary format...
>> 
>> I would do that too. Also I would override 'Read and 'Write in order to
>> make it platform-independent. (Stream_Element should be replaced by
>> octets.)
> 
> No problem with that - there is already a framework in that package (for other 
> files) that sends things byte-per-byte in a deterministic endianess; floats are 
> split/merged with certain a Float_portable_binary_transfer package.

No, I meant your idea of a text-oriented stream. So Float'Write would put
Float in a human-readable format (instead of Put). But of course, a binary
transfer is always preferable.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: Text_IO from a stream

[Simon Wright]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> I would override 'Read and 'Write in order to make it
> platform-independent. (Stream_Element should be replaced by octets.)

How would that particular change help platform independence?

Re: Text_IO from a stream

[Dmitry A. Kazakov]

On Tue, 01 Apr 2008 21:49:41 +0100, Simon Wright wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> I would override 'Read and 'Write in order to make it
>> platform-independent. (Stream_Element should be replaced by octets.)
> 
> How would that particular change help platform independence?

Because then you would control both the representation (T'Write) and the
medium (octet of bits, assuming it atomic as usual).

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de