Re: Why couldn't an operating system be written in ada

[lyttlec <lyttlec@removegmail.com>]

On 2/26/19 3:46 AM, Niklas Holsti wrote:
> On 19-02-25 23:56 , Rabican wrote:
>> On Saturday, July 13, 1996 at 3:00:00 AM UTC-4, Mark  McKinney wrote:
>>> It has been claimed that the capability to interface with other
>>> languages
>>> is a great asset to ada. Sometimes interfacing can be a tremendous
>>> liability. Besides the OS could perform most of work that the language
>>> runtime does. So why not build an OS in ADA?
>>
>> yeah why not?  anything?
> 
> This has been discussed many times before in comp.lang.ada.
> 
> The first question is not "why not build an OS is Ada", the first
> question is "why build a new OS at all"?
> 
> Then, if a new OS is going to be built for some reason, we can ask which
> language should be used, and of course (IMO) Ada would be a strong
> contender. However, for larger systems, the OS must usually implement a
> "process" concept that goes beyond Ada tasking and provides isolation
> between different users and applications. This means that the OS will
> have a process/service-level API that is not, as such, Ada-language
> specific. And so the fact that the OS is implemented in Ada becomes
> invisible on the application level.
> 
> This is not to say that an OS API specified in Ada could not be an
> improvement (for Ada applications) on the current OS APIs which are
> usually specified in C. However, such an Ada OS API could also be
> provided for an OS implemented in C or some other language.
> 
> At present, for small, (mostly) stand-alone embedded Ada systems, the
> bare-machine Ada run-times are sufficient -- and they are usually
> written in Ada. For larger or network-connected systems, where a
> comprehensive OS is needed, the Ada compiler vendors often provide
> run-times that hide the chosen OS (say, VxWorks) from the Ada
> applications, making the OS implementation language irrelevant (as long
> as the OS works).
> 
> There are of course exceptions, such as the RTEMS real-time OS/kernel
> which originally supported Ada run-times but for which I believe there
> is today no vendor-supplier Ada run-time, which means that Ada projects
> that choose to use RTEMS (for some unfathomable reason) have to bind to
> the RTEMS C-level services directly.
> 
>> can ada do CSP?
> 
> Your question is rather vague, but the answer is almost certainly "yes"
> -- the Ada rendez-vous is very similar to an (unbuffered) Occam channel.
> 
As to why write an OS in Ada, read Bruce Schneier's book "Click Here to
Kill Everybody". There is a need for an OS that can be proven correct
and can be scaled down to SBC size. Only a small subset of Ada would be
required to write the kernel. For example, Tasks are not needed to write
a kernel, nor are any POSIX features.
As far as I can tell, the only candidate language for writing such an OS
are Ada and Fortran. (Not too sure about Fortran.)