Date: 30 Jun 1996 20:58:35 -0000
Message-ID: <19960630205835.29571.qmail@koobera.math.uic.edu>
From: djb@koobera.math.uic.edu (D. J. Bernstein)
To: drums@cs.utk.edu
Subject: Re: Obsolete syntax

> I support option 2 as well.

Me too. I agree with Keith that there should be a grammar saying what
you have to accept, and text saying what you can generate. I agree
with Paul that it's a Bad Idea to have two conflicting grammars.

Note that foo/obsolete-foo is only one side of the coin; the other
side is foo/new-fangled-foo. An extreme example:

   year = obsolete-year / current-year / new-fangled-year
   obsolete-year = 1*3DIGIT
   current-year = 4DIGIT
   new-fangled-year = 5*DIGIT

A parser must accept all of these, interpreting obsolete-year by the
rules that we worked out. A generator must not create obsolete-year
because it'll start confusing people in the year 2000. A generator must
not create new-fangled-year because some current parsers can't handle
it; but this rule is scheduled to change in the year 5000.

---Dan