Re: ADA compilers

["Björn Lundin" <bnl@spray.se>]

2005-06-03 kl. 21.12 skrev Patty:

> Yes, we are trying to port an existing application.  I have looked at
> GNAT, but they only have ADA95.
>
We have ported a fairly large system from Ada83 to Ada 95 (Ie using an 
Ada 95 compiler on Ada83 code)
with hardly no problems. The things to watch out for is if you have 
variable names that
are the same as the new reserved words that Ada 95 brings. Ie you cant 
have a variable called 'aliased' since
that is a reserved word now.

We are using Gnat now, and had troble with some applications due to 
circular dependencies,
with the resukt that the Gnat compiler refused to link the application. 
The 'difficult' application contained heavy
use of tasking, in combination of a great deal of generic packages. The 
old compiler said OK, and so did other
Ada 95 compilers. Minor rewrite solved it.

A BIG difference with Gnat and other compilers are the way the Ada 
library a
is handled. We used it a lot, having several libraries in the same 
level, but not able to see each other.
ie
global
     level2-1
     level2-2
        level3
     level2-3

where the ones on level2 could all see global, but not each other. 
Level3 could see level2-2 and global but not the others

Of course, having different packages, with the same name, in all 
level2's is common in our system.
Tcl-script reading flat file'repository' based on current working 
directory, and
use of environment variables ADA_INCLUDE_PATH and ADA_OBJECT_PATH made
it possible to make it work, without having to use several projectfiles.

This was the
biggest challege

Then of course, packages using vendors spcifics, as how to get the 
command line, tasking policies
etc will differ.

Another thing to watch out for, if tasking is inviolved, is how the old 
compiler created tasks.
Is it run by the os like threads or locally in the runtime? This 
changes the way you can interact
with blocking io. We got a big boost using Gnat, because it made it 
possible to use
blocking io, instead of polling.

This was on Aix, but compiled and linked and tested (very very little) 
on Linux and mac os X as well

/Björn

Björn Lundin
bnl at spray dot se