Re: ada -> C translator

[dewar@merv.cs.nyu.edu (Robert Dewar)]

iRichard O'Keefe said

<<Nor has Fergus said that "portable C is portable C and that is that".
His claim, as I understood it, was that one can translate a source
program that is intended to be portable to C that can adapt to particular
targets but is usable on many.  Talking about interfacing to COBOL misses
_his_ point, because in that case the source program isn't _intended_ to
be portable (the porting target might not _have_ a COBOL compiler).>>

I gave many other examples.

The problems that people have in understanding the nature of target
dependence make me think that people do not really understand what we
are talking about. They still probably are thinking in terms of translation
into reasonably high level C, but that's NOT possible. What we are talking
about is generating very low level C, much of it at the level of semantics
of assembly, and much of it incorporating target semantics.

And if you do not think it is possible to write portable Ada programs that
interface with COBOL, you completely misunderstand the intention of section
B.4 of the RM.

Sure it might be the case that a partiular source program does not use this
feature of Ada 95, and you only need a subset of the language compiled.

Well that of course changes the viewpoint. If you restrict the subset
severely enough (no exceptions, pragma suppress assumed, no nested 
procedures, no variant records etc. etc. etc.), then you WILL be able
to translate the Ada subset directly into C.

But if you want to cover the whole language, even if you restrict yourself
to the required part of the language, you will find situations in which you
have to play low level games, and where it is hard, or probably impossible,
to avoid target dependences in the generated C code.