Re: Ada versus Pascal

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

On 2021-10-22 12:59, 711 Spooky Mart wrote:
> On 10/22/21 1:18 AM, ldries46 wrote:
> 
> [...]
> 
>> Ada is stricter
>> than other languages and is meant to have NO Operating system dependant
>> items, so if you cannot go around something there must be a package on
>> each operating system having the same interface everywhere.
> 
> By this do you mean the same syntax and libs will run on all target
> systems without fiddling with {IFDEF} and architecture compiler switch
> woo foo for USES and repetitive cross-arch boilerplate?


I'm not ldries46, but here is an answer: Ada standardizes _some_ 
functions for which some other languages use "OS" services, principally 
threading, which in Ada is the "tasking" feature. Indeed Ada tasking 
works in the same way whichever OS is used, and also in the "bare 
board", no-OS situation. This is very useful for developing 
multi-threaded embedded SW, because the Ada tasking code can be tested 
on desk-top workstations and then executed on the target system 
unchanged. (and no "ifdefs").

But real operating systems (as opposed to simpler real-time kernels) 
provide many services that are not standardized in Ada, for example 
inter-process communication.


> One thing I can't stand about Pascal is the totally different functions
> and logic from several operating systems that MUST be re-written several
> times in the same code base to do the same job. This drives me mad. In
> fact it irks me so much I was thinking of writing some libraries for
> things I do that would handle this all automatically across arches.
> There would go a couple months of Sundays.
> 
> Think IPC with Pascal. Get a good IPC routine going for Linux in your
> app, then you have to re-write it for MAC and Windows, and even some
> other flavors of *nix.


Indeed.


> So am I to understand that the Ada compiler has somehow eliminated this
> problem, by ensuring every target OS has a syntactically conformant
> package to execute its methods using the same statements?


Sadly no.

However, there are some rudiments:

- There is a standardized Ada interface (binding) to POSIX services. 
This is implemented in an Ada library called Florist. If you find or 
make a Florist implementation for the OSes you use, your Ada program can 
use the same OS service interfaces on all those OSes.

- The gcc-based Ada compiler GNAT comes with a GNAT-specific library 
that provides some OS services with the same Ada API on any OS that GNAT 
supports. This includes some IPC, but I don't know exactly how far that 
goes, and the library may of course change from one GNAT version to the 
next.

- There is an Ada library called Win32Ada that provides an extensive set 
of Microsoft Windows services, but it is a "thin binding" meaning that 
even the API is Windows-specific.

The Ada applications I have created and worked with have needed only a 
few OS services, basically some IPC: text in and out via pipes to and 
from a child process. We implemented our own binding to the required OS 
services (pipe and process creation and destruction). The interface 
consisted of a package declaration (.ads file) that was basically the 
same for all the supported OSes (Windows, Linux, Mac OS X) but had 
different OS-specific package body files (implementations, .adb files). 
In practice I think the Linux and Mac OS X implementations were the same 
and used direct binding to fork() and pipe() etc. The Windows 
implementation used Win32Ada.