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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Ada --> C Translation, was: Win CE target
Date: 1998/10/13
Message-ID: <EACHUS.98Oct13164304@spectre.mitre.org>#1/1
X-Deja-AN: 400736123
References: <6u6flv$qn7$1@nnrp1.dejanews.com>
 <360FB3B0.5B0E218C@galileo.mpi-hd.mpg.de> <wcck92nbxdh.fsf@world.std.com>
 <6vobnk$vt9$1@jupiter.cs.uml.edu>
Organization: The Mitre Corp., Bedford, MA.
Newsgroups: comp.lang.ada
Date: 1998-10-13T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <6vobnk$vt9$1@jupiter.cs.uml.edu> dramirez@cs.uml.edu (Dr Amirez) writes:

 > ... If you consider a feature rich language a better language
 > then let me tell you this. I remember seeing a question on this forum 
 > that goes like this: "If a task blocks on I/O, do other tasks get a chance 
 > to run or the *process* will suspend itself, and no task will run 
 > until the process get scheduled again? "
 > Someone responded that it's undefined. Well, I would think such
 > an important feature should be very well defined instead  of being
 > left as an excercise for the user to find out how that is implemented
 > on their systems.

   I suspect that you misheard.  The correct answer is not that it is
undefined, but that it is not defined unless the implementation
supports the Systems Programming Annex. (In particular, section C.3,
Interrupt Support.)

  But this misses the point.  The real reason it is not defined in the
core standard is that for some purposes, you need to be able to
control things like tasking policies.  The Real-Time Systems annex
allows the programmer to change the task dispatching policy.  Also,
some implementations have different run-time libraries available with
support for different policies.  So the real answer is that, if it
matters and you don't like the standard policy, read annex D, and
choose a policy that you do like.

 > After all, isn't Ada intended to be a system programming language?

    Yes, especially if the System Programming annex is supported. ;-)
(Actually, I suspect that most, if not all compilers try to support
annex C.)

 > You can't program systems using features that are system dependant
 > themselves.

   Huh?  The SP annex has nine implementation-defined characteristics
that are required to be documented.  For the most part they are things
which MUST be implementation dependent, such as what interrupts the
hardware has, or the op-codes for machine instructions.

 > The more features a language has, the more flaws it has. You, as an
 > Ada programmer, probably know better than I.

   No, I don't know that.  I do know that if the language is at least
as powerful as Peano arithmetic, it is either incomplete or
inconsistant.  The Ada community puts lots of effort into being
consistant, but does have well marked doors you can use if you need
completeness.
--

					Robert I. Eachus

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