Re: data structures

[Perry Smith <pedz at easesoftware dot com>]

On Apr 17, 2006, at 11:21 AM, Joe Buck wrote:

> On Mon, Apr 17, 2006 at 08:15:13PM +0530, Deepan Chakravarthy wrote:
> > Hello,
> > We are in the process of designing compiler for another language. We
> > use gcc for most part of it. We want to know how classes, inheritance
> > are implemented in g++ . We find that is not separate dot y (.y)  
> > file to
> > list all the grammar rules for C++.  The parser seems to take care of
> > everything.
>
> GCC uses a recursive descent parser for C++.  Releases before 3.4 used
> a Bison (.y, as you call it) parser together with a special pass  
> between
> the lexical analyzer and the parser to try to deal with the fact that
> the C++ grammar is not LR(1), but requires unbounded lookahead (for
> example, to distinguish constructor calls from function declarations).
> After years of trying to make that parser work, it was discarded and
> replaced.
>
> This (the fact that GCC abandoned an automatically generated parser in
> favor of a hand-written one) seems to regularly shock students who  
> have
> recently completed a typical university compiler course; most of these
> courses devote excessive attention to the theory of LR parsing  
> after a few
> disparaging words against recursive descent parsers, taking so much  
> time
> to cover lexing and LR parsing that there's little time for  
> anything else.

That sounds like a fascinating thesis: determine what class of  
languages C++ belongs to and then develop a meta-processor and input  
specification to properly parse C++.