Re: Ada83 equivalents for Ada95

[bobduff@world.std.com (Robert A Duff)]

In article <31927190.35AA@csehp3.mdc.com>,
James A. Squire <m193884@CSEHP3.MDC.COM> wrote:
>Has anybody gone to the trouble of translating code that uses features
>new to Ada95 back into its Ada83 equivalent?  If anyone knows of such
>examples that are available on the Internet, please let me know (email
>or comp.lang.ada).

I don't know of any such effort.

I'm curious as to why you want this.  Do you want to develop Ada 95
code, but then run it on a system where Ada 95 does not yet exist, but
Ada 83 compilers do exist?

It seems pretty difficult, to me.  For example, how do you translate
access-to-subprogram types into Ada 83?  It could be done.  Represent an
access-to-subprogram value as an integer number.  Generate a single
subprogram for each access-type-subtype type.  This subprogram does a
case statement on the integer, and has one branch for every possible
subprogram that might have been called.  The translation tool would have
to do a global analysis of the entire program, to track down every
'Access.  For every subprogram P, if somebody wrote P'Access anywhere in
the program, assign a unique integer to P, and put a call to P in that
case statement mentioned above.

Every such P would have to be declared in the visible part of its
package, even if in the original source, P is declared in the body.

I'm not sure how you would preserve elaboration order, since that
case-statement subprogram will need extra with-clauses to be added.

In any case, such a tool would be approximately as complex as an Ada
compiler -- the same order of magnitude anyway.  If you've gone that
far, why not just write an Ada 95 compiler?

Also, efficiency would suffer.

- Bob