Re: Standard Ada Preprocessor (Was: why ada is so unpopular ?)

["Robert I. Eachus" <rieachus@comcast.net>]

Marin David Condic wrote:

> Most of what's in System seems to be useful only at run time. By then, I 
> could have easily solved the problem for myself by having some kind of 
> app-defined configuration file or similar thing I read in and use to 
> determine which calls to make. So any solution has to happen at compile 
> time or it really doesn't do any good.

My point was that we can fix System to some extent, since Strings can 
now be static.  Of course there is NO universal solution because on some 
systems some values will be static, and on others they won't be known 
until run-time.  But if we "fix" System so that the compiler can 
document such things, then users will be able to do what they can do.

I certainly don't buy the "conditional compilation must happen at 
compile time" argument.  It may be true in most embedded applications 
that you can statically know these things at compile time.  But I also 
deal with creating .dlls that must match the current hardware.  If that 
means that I have to generate self-modifying code, so be it.  (In 
practice I build and install the correct dispatch table when 
initializing a .dll.)

Now it would be nice if I had a compiler that could create a .dll that 
would use x87, 3dNow!, SSE, SSE2, or possibly now SSE3 code as 
appropriate.  I don't.  But assuming I know what I am doing creating the 
correct .dll is not too painful.  (Low-crawling under barbed wire in the 
mud, rather than crawling over broken glass in freezing rain.)

But every once in a while I like to dream about the facility that Ada 
environments were supposed to have had, where I could just say compile 
this code for these dozen hardware specifications, and package the 
result in one load module. ;-)

However, back to the world as it exists.  The discipline of Ada is that 
you should be able to push most, if not all, hardware dependencies first 
into package and other unit bodies, and then into variant parts and if 
statements.  It is hard word to do that.  But IMHO it is much easier to 
maintain than you can ever save during development by not doing the work.

So I don't believe in preprocessors for Ada code.  There are times that 
I do get frustrated at the fact that I can put case statements in type 
declarations and sequences of statements, but I can't wrap a single 
declaration in one.  But usually after a short break, I come back and it 
wasn't necessary after all.

-- 
                                           Robert I. Eachus

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