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To: David Carlton <carlton@math.stanford.edu>
cc: gdb <gdb@sources.redhat.com>
Subject: Re: c-exp.y 
In-Reply-To: Message from David Carlton <carlton@math.stanford.edu> 
   of "Tue, 17 Dec 2002 13:59:07 PST." <ro1y96omhn8.fsf@jackfruit.Stanford.EDU> 
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Date: Wed, 18 Dec 2002 19:36:00 -0000
From: Paul Hilfinger <hilfingr@CS.Berkeley.EDU>
X-SW-Source: 2002-12/txt/msg00285.txt.bz2


> I have heard that C++ parsing is a royal pain, but I'm not sure that's
> the issue here: I suspect that GDB's problems are at a more basic
> level.  I suspect that the division of labor between what the
> parse_expression does and what eval_expression does is a bit funny,
> and I'm pretty sure that the rule
> 
>   start   :     exp1
>           |     type_exp
>           ;
> 
> in the parser leads to some conceptual incoherence.  

It does, but it is not alone, which I guess was my point.  Look
further down in the grammar, and you find

    exp	:	'(' type ')' exp  %prec UNARY
			     ...
	    ;

    exp	:	'(' exp1 ')'
		{ }

which is essentially the same thing all over again.

The point is that there are instances in the C/C++ grammar that require
knowing whether a given identifier or qualified name is or is not a
type, which is why this sort of stuff tends to migrate into lexical
analysis.  

Paul Hilfinger