Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!apple!mips!lai
From: lai@mips.COM (David Lai)
Newsgroups: comp.sys.mips
Subject: Re: MIPS YACC commedations and question
Message-ID: <32377@gumby.mips.COM>
Date: 29 Nov 89 17:26:24 GMT
References: <2168@cs-spool.calgary.UUCP>
Reply-To: lai@mips.COM (David Lai)
Distribution: na
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 36

In article <2168@cs-spool.calgary.UUCP> cliff@.UCalgary.CA (Cliff Marcellus) writes:
>
>  Well now the (not so) down side... does anyone know what a configuration
>  in a state of the form :
>
>  expression : expression PLUSOP $$56 error
>
>  means?  (I don't know what "$$56" is supposed to do for me, and it's
>  not in the documentation -- at least I can't find it.)
>--
>Cliff Marcellus                UUCP     : {any backbone}!calgary!ssg-vax-a!cliff
>Dept of Physics and Astronomy  DOMAIN   : cliff@ssg-vax-a.phys.UCalgary.CA
>The University of Calgary      SPAN     : CANCAL::CLIFF                 

The $$56 is a generated reduction resulting from an action embedded in the
reduction rule, ie:

expression: expression PLUSOP { a=12; b=13; $$=100; } error
	{ $$ = $3; }
	;

would be translated to two reductions:

expression: expression PLUSOP $$1 error
	{ $$=$3; }
	;

$$1:
	{ a=12; b=13; $$=100; }
	;

The value of $$1 in the first rule's action ($3) is the value assigned
to $$ in the second rule's action.
-- 
        "What is a DJ if he can't scratch?"  - Uncle Jamms Army
     David Lai (lai@mips.com || {ames,prls,pyramid,decwrl}!mips!lai)