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From: vlsivie!mike@relay.EU.net (Michael K. Gschwind)
Newsgroups: comp.compilers
Subject: Re: Lexers in YACC?
Keywords: yacc, lex
Message-ID: <9009101344.AA20458@vlsivie.tuwien.ac.at>
Date: 10 Sep 90 22:44:06 GMT
Sender: compilers-sender@esegue.segue.boston.ma.us
Reply-To: Michael K. Gschwind <vlsivie!mike@relay.EU.net>
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Lines: 34
Approved: compilers@esegue.segue.boston.ma.us
In-Reply-To: <26E50E36.34BE@marob.masa.com>

In article <26E50E36.34BE@marob.masa.com> you write:
>What I don't understand is how to make the generated parser of the first
>stage "return" tokens to its caller.  It seems to require generalized
>co-routines, which of course C does not provide.  The operating system is
>Unix System V.

No, you don't want to do this. Rather, I would queue the tokens, insert 
magic tokens (which make the grammar LALR(1)) and after the first stage 
call the second. Sequence works fine as long as there is no interaction.
In the above scenario, there is no need for interaction.

BTW, in many cases, lex is powerful enough to make a grammar lalr(1)
with right context rules. You want to look into these. If these aren't
sufficient, you could use start states as well.  
E.g., if you have to differentiate between function definitions,
function declarations and variable dfinitions in C, you could use:

%%
{identifier}/\([^)]\)			return FUNCTION_DEFINITION;
{identifier}/\([^)]\);			return FUNCTION_DECLARATION;
{identifier}				return VARIABLE; 

%%

			bye,
				mike

Michael K. Gschwind             mike@vlsivie.at
Institute for VLSI-Design       mike@vlsivie.uucp
Technical University, Vienna    e182202@awituw01.bitnet
Voice: (++43).1.58801 8144      Fax:   (++43).1.569697
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