Re: 9X and the NEED for preprocessing

[stt@inmet.inmet.com]

With regard to Ada preprocessors, and Ada9X:

First of all, preprocessors create no optimization problem,
since they operate at the lexical, or possibly syntactic, level,
long before the optimizer takes a look at the program.

However, I am not a great fan of Ada preprocessors.
We have implemented a compiler system and development tools
for 6 targets and 7 hosts without using a preprocessor.
Our general strategy is to define one or more target/host-independent
package specs with target/host-dependent bodies.
We minimize the size of such packages, and simply reimplement
them for each distinct target/host.

Sometimes, the package spec is target/host-dependent as well,
but only in its definitions, not in the names defined (e.g.,
one host might define the type "Link_Name" as being an 8 character string,
another might define it as being a 30 character string).

The net effect of this approach is that a particular configuration
is determined by a set of source files, not a set of preprocessor
switches.  Also, for cases where we do restrict differences to bodies,
we can select a different configuration at link time by choosing
a distinct "implementation catalog variant" (in Intermetrics AIE-speak),
requiring no recompilation.

Anyway, so much for truth and beauty.  If there is a compelling
argument for a standardized preprocessor, I am sure that the Ada9X
process will be willing to consider it, even though the "official"
public revision request period is over.  The Ada9X process is
going to include a number of public reviews, and the various
project teams working on Ada9X will continue to keep their
ears open for brilliant and/or urgent proposals.

S. Tucker Taft  (Ada9X DR -- aka "distinguished" reviewer)
Intermetrics, Inc.
Cambridge, MA  02138