Path: utzoo!attcan!uunet!cs.utexas.edu!usc!ucsd!helios.ee.lbl.gov!austern@ux5.lbl.gov
From: austern@ux5.lbl.gov (Matt Austern)
Newsgroups: comp.lang.misc
Subject: Re: The Universal Language
Message-ID: <6465@helios.ee.lbl.gov>
Date: 13 Aug 90 18:24:58 GMT
References: <24043@megaron.cs.arizona.edu>
Sender: usenet@helios.ee.lbl.gov
Reply-To: austern@ux5.lbl.gov (Matt Austern)
Organization: Lawrence Berkeley Laboratory (theory group)
Lines: 24
X-Local-Date: 13 Aug 90 11:24:58 PDT
In-reply-to: gudeman@cs.arizona.edu (David Gudeman)

In article <24043@megaron.cs.arizona.edu>, gudeman@cs (David Gudeman) writes:
>I am always disturbed by the idea that for a language to have some
>good property, it must forbid the programmer from doing X.

I'm sure that this is obvious to everybody, but I think it bears
repeating: if the "good property" is efficiency, this is often best
achieved by forbidding the programmer from using certain
constructions.

The more assumptions a compiler can make about a program, the better
it can do the optimization, and in many cases, the only way a compiler
can safely assume that a programmer doesn't do something is to make it
illegal.  (The C calling convention is more complicated than the
FORTRAN calling convention, for example, because C allows recursion.
Can you really imagine a C compiler/linker that can prove that a
program has no recursive calls, and use a simpler calling convention
for such programs?)

There really is a tension between flexibility and ease of
optimization, and the resolution isn't necessarily the same for all
purposes. 
-- 
Matthew Austern    austern@lbl.bitnet     It's not very subtle, but, uh, 
(415) 644-2618     austern@ux5.lbl.gov    neither is blowing up a whole school.