Re: Ada "library only" compiler ?

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 12-07-21 03:27 , Randy Brukardt wrote:
> "Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message
> news:a6tvrmFdinU1@mid.individual.net...
> ...
>>> So again, I don't mean to be harsh but if we are always building on C
>>> through the GNAT compilation progress would it be logical to decouple
>>> the two to create a simple Ada "as library" compiler? It seems that
>>> we can't open a file or get a command line argument without C
>>> anyways.
>>
>> GNAT runs on operating systems (Windows, Linux, etc.) in which the
>> Application Programming Interface is defined in C. In order to open a file
>> under Linux, the application (here GNAT) *must* use the open() or fopen()
>> functions, which are defined in the API as C functions. Trying to open a
>> file using "low-level Ada" would be breaking the OS interface which is
>> obviously a bad idea (and probably impossible because an application does
>> not have the necessary low-level access rights for that).
>>
>> Likewise, when a GNAT-compiled Ada program runs on Windows or Linux and
>> accesses files, the GNAT-provided libraries (Ada.Text_IO etc.) must use
>> the Windows/Linux C-style I/O libraries, for the same reasons.
>
> This isn't quite right. Janus/Ada contains 0% C code (there is not a single
> line of C in Janus/Ada, the only exception being the never released Sun OS
> compiler and some parts that Unisys built for their hardware). That's true
> even on Windows. The Windows Win32 API does not require using any C code; it
> can be accessed directly. (Even the calling convention is not "C", it's
> "StdCall" which originally was "Pascal" until Microsoft got rid of their
> Pascal compiler.)
>
> It's true that the Win32 API is defined in C, but an Ada system can
> interface directly to it without using any intermediate C code.

Sure. I didn't say that the compiler or other Ada program must contain 
some C source; I said that it must use the OS API, which is almost 
always defined in C (unless it chooses to use the low-level, 
machine-specific OS-invocation mechanisms, as Peter Chapin pointed out).

Still, I have sometimes found it easier to write a thin interface layer 
in C, as I also said, just to have a simpler Ada/C interface.

> Janus/Ada is written solely in Ada; the Janus/Ada runtime is about 95% in
> Ada and 5% in assembler.

But you still use the Win32 C API and its services, translated into Ada 
form. Which is nice, if you can afford the effort (including the 
maintenance effort).

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .