W3C home > Mailing lists > Public > public-rdf-wg@w3.org > December 2012

Re: Left-recursive LALR(1) grammar for turtle (ACTION-217)

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Mon, 10 Dec 2012 10:51:36 +0000
Message-ID: <50C5BEB8.5070007@epimorphics.com>
To: public-rdf-wg@w3.org
The issue raised is wanting to add to the useablity of grammar for LALR 
parser generators.  Object lists do not have this problem because comma 
is a separator, and you can't have a trailing ",".

As this useability rewrite is at odds with a grammar for top down (RC or 
LL) usage, we can't have both.


Publish the grammar as it is in the LC version (which is the same as 
SPARQL 1.0) and also add a note for this rule that explains a way an 
LALR generator might be applied, quoting the rule below, aligned in 
names to the published grammar.

On 08/12/12 15:53, Sandro Hawke wrote:
> polist
>      : predicate olist
>      | polist SEMI
>      | polist SEMI predicate olist
>      ;

We should note this a an expected shift/reduce conflict.  See section 
5.2 [1] of the bison manual for how that's hanlded in this rather common 
case.  By default it does one token lookahead (AKA it behaves like an LL 


[1] http://www.gnu.org/software/bison/manual/bison.html#Shift_002fReduce
Received on Monday, 10 December 2012 10:52:06 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 22:02:09 UTC