Re: Ada 95 grammar for aflex?

[Cesar Rabak <csrabak@uol.com.br>]

Robert Dewar wrote:
> 
> In article <3A69BA8F.A26A531E@uol.com.br>,
>   Cesar Rabak <csrabak@uol.com.br> wrote:
> > On your lines it continues with "...C++ was not a new
> > experimental language, it was an almost compatible superset
> > of C - and at that tim nobody had been able to write an
> > LARL(1) grammar for C. The LARL(1) grammar used by ANSI C was
> > constructed by Tom Pennello about a year and
> > half later - far too late to benefit me and C++."
> 
> I find that a bit odd, there has been no problem in
> constructing the necessary grammars for parsing C with these
> kind of tools, and they have been around for years, but that's
> not the issue.
> 
> The issues are
> 
> a) these tools generate rather slow parsers. This is fixable.
> 
> b) these tools generate junk error messages. This is also
> quite fixable. GNAT gives better error messages than Ada/Ed,
> but at the time, people regarded Ada/Ed as having excellent
> error messages, among the best around.

We agree on these.

> 
> If you are not interested in error recovery, there is
> absolutely no difficulty in writing a table driven parser
> for C++. The problem with g++ is that it has grown rusty
> with all kinds of kludges, and no one has had the nerve
> to redo it from scratch which is what was needed :-)

So we're detecting an opportunity for improvement! 

> 
> To be fair, many other C++ compilers give equally horrible
> error messages, but they do not seem to suffer from the time
> penalty in parsing to such an extent.

I never thought about this, and in fact with the monolithic binaries
they come I can't figure a way to benchmark the parsing of other
compilers.

> 
> Parsing should take zero time. In my assembly language scanner
> and parser for Ada 83, which runs at something approaching
> ten million lines a minute on a fast PC, perhaps more, I have
> not run it for a while, parsing takes less than 10% of the
> total time (the rest is I/O and lexical analysis).

Taking in account the functions of the parser, it makes all sense to me.
In fact it could be considered one of the "quality attributes" of a
compiler! So bad life is not so easy.

Cesar