Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!munnari.oz.au!goanna!ok
From: ok@goanna.oz.au (Richard O'keefe)
Newsgroups: comp.lang.c
Subject: Re: problems/risks due to programming language
Message-ID: <2919@goanna.oz.au>
Date: 27 Feb 90 04:16:20 GMT
References: <1597@awdprime.UUCP> <8133@hubcap.clemson.edu> <2903@goanna.oz.au> <18033@rpp386.cactus.org>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 40

In article <18033@rpp386.cactus.org>, woody@rpp386.cactus.org (Woodrow Baker) writes:
> In article <2905@goanna.oz.au>, ok@goanna.oz.au (Richard O'keefe) writes:

In fact the section which follows was QUOTED by me, not WRITTEN by me.
Please net.people, do take care with your attributions.

I _did_ write
> > (a) can't be done without introducing a goto or return, or rewriting
> >     the code.
to which Woodrow Baker responded
> Wrong.  you can always set a flag within the various cases and test it at
> the bottom or top of the loop.  Yes this qualifies as re-writing the code.

It seems very odd to say "Wrong" and then admit two sentences later that
it isn't wrong at all.  Look, you can program _any_ can of spaghetti you
like with _one_ loop, _one_ switch, and _one_ flag variable.  The goal is
code that can be read and understood without too much strain; post hoc
flag variables are even worse for that than undisguised gotos.

In Ada, the method of quitting a loop early is the exit statement:
	<Ada LRM 5.7 para 2>
	exit_statement ::= EXIT [loop_name] [WHEN condition];
With no loop_name, it exits the innermost loop.
With a loop_name, it exits the loop labelled with that loop_name.
An equivalent for C would be a set of macros like

	loop(LoopName)
	    break_loop(LoopName)
	end_loop(LoopName)

which could be implemented thus:

	#define loop(X) {
	#define break_loop(X) goto X
	#define end_loop(X) ;X:;}

This does amount to bending the syntax of C, but I think it may be an
excusable case.  The proper nesting of these macros can be easily checked
by a simple tool, and it gives us a disciplined way of using the language
we already have.