Re: Standard Ada Preprocessor

[Marin David Condic <nobody@noplace.com>]

A simple case: Suppose you are developing for an embedded box but you 
want to do some simple "Smoke Testing" on a PC. For the embedded box, 
you need a rep clause for some register. For the PC you're dummying that 
up with something and don't want a rep clause at all. (Or the PC 
compiler barfs on the rep clause that the embedded compiler accepts.) It 
would be nice to say "If compiling for the PC with Aonix, use this code 
(no rep), but if compiling for the target with the Gnat compiler, go use 
that code..."

I've also run into situations where the hardware weenies are working as 
fast as we software bozos are and every few weeks, you're getting new 
turns of a board with different hardware in it. You still need to 
compile for earlier boards but now you have something different - 
probably with a different rep clause. I don't want to go into some 
complex CM and build process just for the developmental stuff - I just 
need a quick and dirty answer to being able to get the code to work on 
two (or more) boxes short-term.

That's why I'm saying that conditional compilation may be ugly and 
intellectually unsatisfying and not "The Perfect World" but often you've 
got circumstances that make it the best, expedient choice for fixing a 
real world situation. And yes, I agree it can be abused. Maybe there is 
some way of making it simple enough to get a job done but not powerful 
enough to make an atrocity.

But its been observed that there never has been a programming language 
in which it has been the least bit hard to write bad code. Maybe we can 
just accept that and live with it.

MDC


tmoran@acm.org wrote:
> 
>   I don't understand what you use rep clauses for.  I normally use them
> when a data structure must be shared outside my program, by a hardware
> device, an OS call, another program, etc.  For those, the rep clause does
> not change when you change compiler or target machine - unless your target
> *requires* a change because it demands a different representation.  Not
> even a perfect compiler could do that automatically.


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