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Path: utzoo!watmath!clyde!cbosgd!ihnp4!stolaf!umn-cs!herndon
From: herndon@umn-cs.UUCP
Newsgroups: net.lang
Subject: Re: structured assembler vs. C
Message-ID: <7500005@umn-cs.UUCP>
Date: Sun, 16-Feb-86 20:59:00 EST
Article-I.D.: umn-cs.7500005
Posted: Sun Feb 16 20:59:00 1986
Date-Received: Tue, 18-Feb-86 03:47:11 EST
References: <401@ccivax.UUCP>
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Nf-ID: #R:ccivax:-40100:umn-cs:7500005:000:1689
Nf-From: umn-cs!herndon    Feb 16 19:59:00 1986



<** Pet Flame On **>
  Actually, it didn't hasn't always been impossible to construct
jump tables in C.  In the Good ol' Days before 0 AL (After Lint),
the "goto" statement would take any operand as a destination.
A label simply had a machine address as a value, and "goto" simply
jumped there.  Thus one could do things like:

foo() {
a:
	bar(a);
}

bar (x)
{
	goto x;
}

and blow one's stack out of the water.  All kinds of unsavory things
were possible, and generally undesirable.  Unfortunately, with the
coming of "strong typing" (and its concomitant weak ideas), the
type label got lost.  One cannot type coerce a label to anything else,
nor anything else to a label.  Very discouraging to those of us who
occasionally like to jump to arrays full of machine code (say, for
direct interpreters, etc.).  Admittedly, these kinds of applications
are generally pretty rare, but doing it now requires an array of
procedure addresses, and one often has to use an enormous stack
if each procedure calls the next.  This is may not be desirable if
there is no reason to return to the caller, as in tail recursion.
It's not optimized in C compilers like it often is in lisp.
  Having a type "label" for type coercions, like the type "void",
would be very useful to me in occasional, rare applications.
  Oops!  Don't get me wrong -- I like strong type typing in practice.
It has saved me countless bugs which would have had me stymied for
days.  However, the "theory" of strong typing as it exists seems
very weak.  Maybe someday, it will get better, but since it appears
closely related to semantic issues, I doubt it.
<** Pet Flame Over **>


				Robert Herndon
				...!ihnp4!umn-cs!herndon