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From: diamond@diamond.csl.sony.junet (Norman Diamond)
Newsgroups: comp.lang.misc
Subject: Re: Language Design, or: is C's Grammar Context Free
Keywords: BNF, Grammars, Silliness
Message-ID: <10151@socslgw.csl.sony.JUNET>
Date: 10 Apr 89 02:14:27 GMT
References: <5200040@m.cs.uiuc.edu> <12443@watdragon.waterloo.edu> <6541@bsu-cs.UUCP> <920@m10ux.ATT.COM>
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Reply-To: diamond@diamond. (Norman Diamond)
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In article <920@m10ux.ATT.COM> mnc@m10ux.ATT.COM (Michael Condict) writes:
>Consider instead the one that someone else posted:
>
>	{ T * x; . . . }
>
>...  One of the following two different parse trees
>should be produced:
>
>		  *                   decl
>		/  \                 /    \
>	       T    x		    T      *
>					   |
>					   x

Those are not parse trees.  Parse trees would resemble the following
ones.  Actually K&R's grammar would produce more complicated trees
than these, but a more complicated grammar could produce these trees.

		expr                 decl
               / | \                / | \
	      T  *  x              T  *  x

And it really isn't difficult to unify these cases to allow an
unambiguous grammar, leaving the resolution to the semantic stage.

		expr_or_decl
		/    |    \
	       T     *     x

Of course, C is ugly because of the difficulty human readers have
in reading such things, but compilers (C compilers anyway) have no
sense of aesthetics.
Norman Diamond, Sony Computer Science Lab (diamond%csl.sony.jp@relay.cs.net)
  The above opinions are my own.   |  Why are programmers criticized for
  If they're also your opinions,   |  re-inventing the wheel, when car
  you're infringing my copyright.  |  manufacturers are praised for it?