Re: Ada Operating System

[Darren New <dnew@san.rr.com>]

Adrian Hoe wrote:
> Sometime ago, I was thrown a question while giving talks in
> Universities. "What language do they use to build the Ada compiler?"
> and an (assumed) answer from the audience was "C". Then raised another
> question: "If Ada has many safety features that C does not have and
> the Ada compiler was written in C, how exactly safe is Ada?"

It's possible for the Ada compiler to be unsafe yet the code it
generates is safe, yes? That is, if the compiler crashes, is that
considered a safety-critical failure? I wouldn't think so, but I don't
write safety-critical code.

In any case, regardless of what you do, the code you generate eventually
turns into machine language, and is therefore only as "safe" as the
underlying machine. Language safety comes from preventing a programmer
from stepping outside the defined semantics of the language. It doesn't
really matter what language you use to check whether a program is safe;
it only matters what language you are checking.

If you wrote a C compiler in Ada, would C suddenly become "safer"? No,
of course not. So why would an Ada compiler in C be less safe?

Richard wrote:
>  It seems that, for the compiler under discussion, things such as
> integer overflow, etc. were not directly addressed. 

This is yet another question, which is how one generates the machine
code using other tools, and how safe those tools are. I.e., this is
confusing "the code the compiler's written in" with "the code the
compiler generates", whereas the question seemed to be about "the code
the compiler's written in" vs "the code the compiler understands how to
compile". Three different systems there - Input, Compiler, and Output.
Depending on how the compiler's built, the output may be more or less
easy to get "right", i.e., accurately reflecting the semantics of the
input.

-- 
Darren New 
San Diego, CA, USA (PST). Cryptokeys on demand.
  To the user, everything works just as expected,
    assuming the user's expectations are correct.