Date: Thu, 28 Nov 1996 14:55:33 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: jkh@time.cdrom.com (Jordan K. Hubbard) Cc: terry@lambert.org, hackers@freebsd.org Subject: Re: Lex/Yacc question Message-ID: <199611282155.OAA01125@phaeton.artisoft.com> In-Reply-To: <11590.849149149@time.cdrom.com> from "Jordan K. Hubbard" at Nov 27, 96 06:45:49 pm
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> > PS: Why isn't there a Lex or Yacc FAQ?
>
> Because they both have more than ample manuals in the 4.4 doc set? I
> dunno - I never really saw a need for FAQs, and I've written quite a
> few parsers (including the entire parser for an ANSI C interpreter I
> wrote a few years back). It's very straight-forward to use both tools
> if you understand the basics of parser operation, and if you don't
> think you probably don't really need to use Lex and Yacc anyway. ;-)
I've written a number of parsers, too. Nonen of them needed:
KEYWORD rest of stuff to end of line
Like the "HELO" keyword in RFC821 requires...:
-------
telnet smtp.lambert.org smtp
Trying 137.190.16.16...
Connected to smtp.lambert.org.
Escape character is '^]'.
220 smtp.lambert.org Sendmail 4.1/SMI-4.1.1 ready at Thu, 28 Nov 96 14:52:19 MST
helo foo foo foo
250 smtp.lambert.org Hello foo foo foo (host.lambert.org), pleased to meet you
quit
221 smtp.lambert.org closing connection
Connection closed by foreign host.
-------
This is for historical compatability with hand-coded RFC821 parsers,
implemented as a C++ encapsulation class for an RFC821 transport
subclassed from a transport facility:
class RFC821_channel : protected Transport {
enum { STATE_PENDING, // no connection
STATE_READY, // connected, no HELO/EHLO
STATE_HELLO, // seen HELO
...
};
private:
int state; /* current command state*/
public:
...
};
Then I subclass TCP/IP, NITS, X.25, etc. from this...
The RFC822 is an envelope parsing (input), cannonizaton (output)
mechanism.
RFC1341/RFC1342 is a subclass of the RFC822 envelope class for formatting
the body pointed to by the envelope class using RFC822 envelope header
items... ie:
MIME-Version: 1.0
Content-type: audio/basic
Content-transfer-encoding: base64
The "MIME-Version:" header from 1341 also needs "text to end of line"
recognition. I'm not working on an RFC1341 lexing/grammar (yet).
I'm astonished that no one has done this all before. It seems so obvious...
Regards,
Terry Lambert
terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.
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