Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!husc6!mailrus!wasatch!utah-gr!uplherc!esunix!bpendlet
From: bpendlet@esunix.UUCP (Bob Pendleton)
Newsgroups: comp.arch
Subject: Re: Semantics (was Software Distribution)
Message-ID: <1000@esunix.UUCP>
Date: 10 Oct 88 14:48:53 GMT
Article-I.D.: esunix.1000
References: <13914@mimsy.UUCP>
Organization: Evans & Sutherland, Salt Lake City, Utah
Lines: 47

From article <13914@mimsy.UUCP>, by chris@mimsy.UUCP (Chris Torek):
> In article <16603@shemp.CS.UCLA.EDU> casey@admin.cognet.ucla.edu
> (Casey Leedom) writes:
>>  As Steve pointed out, what we're probably dealing with is a
>>misunderstanding about the usage of the word "define".
> 
> Probably true.  Someone wanted a Machine Independent Intermediate
                  ^^^^^^^

Fame is so short lived. Leave the discussion for 48 hours and you
become just an anonymous "someone."

> Language to include assertions that would pin down the exact action of
> various `undefined' actions (1/0, *(type*)NULL, etc).  I claim that
> this is, or should be, unnecessary (regardless of the feasibility of
> MIILs).  That these actions are `defined as undefined' is not self
> contradictory, but it certainly does make for misunderstandings!

Before I go on let me say that I've realized that I've been using the
term portable to mean machine independent. Where portable should mean
something like "can be moved to a new machine with some effort", and
machine independent should mean something like "can be moved to a new
machine with at most a recompilation."

Defined as undefined is a perfectly valid way to define the actions of
an operand on particular subranges, like * on NULL and square root on
negative numbers.  But, from the point of view of trying to make
programs machine independent it is a useless definition. This kind of
definition forces me to test a program on every existing machine
architecture, using every existing compiler for each architecture, and
even on every new release of each compiler, before I can claim that
the program is machine independent. Using a language that has features
that are defined as undefined and limited resources I can have no
assurance that the program is machine independent. I can only hope
that it is portable.

Clearly, I hope, there is a gap between the goals of a MIIL (Machine
Independent Intermediate Language) and a langauge that is defined in
such a way as to be machine dependent. This gap requires that the
machine dependent parts of such a language must be bound to MIIL
dependent definitions before the language can used as a source
language for compilation to MIIL.
-- 
              Bob Pendleton, speaking only for myself.
An average hammer is better for driving nails than a superior wrench.
When your only tool is a hammer, everything starts looking like a nail.
UUCP Address:  decwrl!esunix!bpendlet or utah-cs!esunix!bpendlet