From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <406C42A4.8000607@swtch.com>
From: Russ Cox <rsc@swtch.com>
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To: 9fans@cse.psu.edu
Subject: Re: [9fans] multiple inputs
References: <cc59a5b4b981440e405f12822643ee6b@vitanuova.com>
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Date: Thu,  1 Apr 2004 11:26:12 -0500
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rog@vitanuova.com wrote:

>>What do the 9fans think of hygenic macros?
>>    
>>
>
>dunno what others think but i reckon macros (hygienic or not) make it
>much harder to maintain a program.  you have to get through the custom
>syntax before you can start seeing what's really going on.
>
>if you need that kind of expressivity, consider writing an
>interpreter, a translator or a preprocessor.
>  
>

I think it would be great if the C compiler had some sort
of nice extension facility (call it hygenic macros with syntax) so that
we could write

alt {
<- done =>
    print("done\n");
c <-= val =>
    print("sent val\n");
}

But you're right, that would make it much harder to maintain
the program.  Instead we should content ourselves with writing

Alt alts[3];
alts[0].c = done;
alts[0].v = 0;
alts[0].op = CHANRCV;
alts[1].c = c;
alts[1].v = val;
alts[1].op = CHANSND;
alts[2].op = CHANEND;
switch(alt(alts)){
case 0:
    print("done\n");
    break;
case 1:
    print("sent val\n");
    break;
}

which is much clearer and doesn't require us to wade through
custom macro syntax.

Russ