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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Any research putting c above ada?
Date: 1997/05/01
Message-ID: <EACHUS.97May1150917@spectre.mitre.org>#1/1
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References: <5ih6i9$oct$1@waldorf.csc.calpoly.edu>
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Organization: The Mitre Corp., Bedford, MA.
Newsgroups: comp.lang.c++,comp.lang.c,comp.lang.ada
Date: 1997-05-01T00:00:00+00:00
List-Id: <comp.lang.ada>



In article <5k8b0p$25f2@uni.library.ucla.edu> jmartin@cs.ucla.edu (Jay Martin) writes:

  > Huh?  By definition, if the subject has to do with practical
  > software construction then that is in software engineering.  If it
  > is worthless theoretical masturbation, then that of course lies in
  > the domain of Computer "Science".

    If you want to say that software engineering is about practical
software construction, fine.  But if you don't know how to navigate
around the slippery shores of the halting problem, or NP-completeness,
you will spend an awful lot of time trying to solve problems that are
not practically solvable.  

    Notice the wording there--if you know how
and where to draw the line, you can solve your problem without
generalizing it into a "simpler" case that is out of reach.  Or, if
you know what you are doing you can, with little trouble, solve an
NP-complete problem.  For example, Ada compilers are required to solve
bin packing problems.  In general, the bin packing problems the
compiler sees are easy to solve, and if you go to the effort of
embedding a large and difficult problem in your record representation
clause, well compiling it might take a while.

   Another example in an Ada context is the discussion we just had
about elaboration order.  In theory, finding a "good" elaboration
order for any Ada program is equivalent to the halting problem.  In
practice, any compiler can find a legal order, and most compilers will
find a "good" order for most programs.  (A good order here is one
which does not raise Program_Error for any input.)

   And by the way, don't ask for the compiler to reject any program
that doesn't run to completion.  In this end of the programming
business we have tools which reject programs that can be shown to halt
for any reason.  Of course, I can't prove that any arbitrary embedded
program never halts, but I don't want to.  What I want is a set of
rules so that my programs can be shown never to halt.  That is a
possible (and not too difficult) task.

--

					Robert I. Eachus

with Standard_Disclaimer;
use  Standard_Disclaimer;
function Message (Text: in Clever_Ideas) return Better_Ideas is...