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From: robert_dewar@my-dejanews.com
Subject: Re: should I be interested in ada?
Date: 1999/02/19
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In article <7ajv17$mrf$1@nnrp1.dejanews.com>,
  dennison@telepath.com wrote:
> Since Fortran's parallel loops are just loops with extra
> semantics about what dependencies exist between
> iterations, wouldn't it be possible to do the same thing
> in Ada with new loop pragmas? (eg: prama
> No_Loop_Carried_Dependencies (Loop_Label);) Would such a
> scheme render the compiler non-conformant?


Well you can always make arbitrary extensions by using the
fiction that they are pragmas, and this particular form of
the pragma is in fact quite a respectable one, but it is
not what I would choose, I would prefer to have a clear
statement that the branches can be done in parallel, not
some rather peculiar statement with unfamiliar terminology
from which this can be deduced!

As for non-conformance, you can simply implement

   for all K in ... loop

and that is still no problem as long as its recognition is
controlled by a switch, e.g. something like --pedantic in
GNU C. So there is never an issue with conformance in
such extensions.

Actually implementation defined pragmas are a rather
pernicious form of language extension, that leaves ISO
Ada even more susceptible to uncontrolled extension than
in COBOL. In COBOL, you have to have a flag that restricts
implementation defined extensions, but there is no such
requirement for Ada with respect to pragmas.

GNAT has added the Restrictions identifiers:

   pragma Restrictions (No_Implementation_Pragmas);
   pragma Restrictions (No_Implementation_Attributes);

but unfortunately these identifiers are themselves
implementation defined. It would be nice if every compiler
would at least adopt these two restriction identifiers.

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