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From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.lang.misc
Subject: Re: How to make a language downward-extensible?
Message-ID: <7950@scolex.sco.COM>
Date: 30 Sep 90 08:42:43 GMT
References: <1990Sep24.160705.21113@newcastle.ac.uk> <9363:Sep2521:41:1290@kramden.acf.nyu.edu> <7935@scolex.sco.COM> <29047:Sep2816:51:1290@kramden.acf.nyu.edu>
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In article <29047:Sep2816:51:1290@kramden.acf.nyu.edu> brnstnd@kramden.acf.nyu.edu (Dan Bernstein) writes:
>> Ugh.  Are you then going to standardize *everything*?
>
>What are you talking about? The only thing added to the language is the
>quickpick control structure. All I'm doing is letting the programmer
>give the compiler a much better chance to optimize a section of code.

Uhm... where are you going to define the names that are used?  Or is the
compiler supposed to go through your "worst-case" one, analyze it, and see
which instruction matches it most closely?  If it could do that already, you
wouldn't need to bother with your "quickpick" thingy.

If the "names" are going to be "standardized" (which is what I was referring
to), you're going to have a real mess on your hands, which is why I went
into the example about the elxsi et al.

>No, it isn't, for the several reasons I explained in the first article
>of this thread. ifdefs are clumsy to define, and they guarantee that
>your program will run poorly when the hardware changes under your nose.

So will your method.  You would have to recompile.

If you do something like:

	#ifdef	BIT_COUNT_IN_HARDWARE
		__builtin_bitcount (whatever);
	#else
		whatever
	#endif

what is the difference between *that*, and your method?  Other than niggling
little details?

>They require that someone who wants to install the software on a new
>machine figure out each one of your ridiculously many ifdefs. That is
>not the portable downward extensibility that we want.

Your method requires lots of things, too.  Generally, though, the person who
builds the compiler would figure them out, not necessarily the installer.
For example, in <stdlib.h> (or something like <stdext.h>, I guess), with the
correct defines for the machine.  No more difficult than installing a libc.

For most people, that is.  Maybe not you.

-- 
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Sean Eric Fagan  | "Never knock on Death's door:  ring the bell and 
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