[antlr-interest] Re: SQL grammar, help on ambig warns
Terence Parr
parrt at jguru.com
Fri Aug 30 15:57:12 PDT 2002
On Friday, August 30, 2002, at 02:19 PM, Ruslan Zasukhin wrote:
> on 8/26/02 23:59, lgcraymer at lgc at mail1.jpl.nasa.gov wrote:
>
>>> I just do all my best to keep grammar k=1 and avoid syntax
>> predicates to get
>>
>> The k value affects ANTLR grammar analysis much more than it affects
>> generated code. Setting k=50, for example, can cause the analysis to
>> take "forever" to generate code from an input grammar, but the
>> generated code does not change (if k is already large enough to remove
>> ambiguities). In your case, k=2 may be a good choice: "LPAREN
>> unsigned_integer" may not be ambiguous.
>
> I have just only read this words.
>
> This is totally new info for me!
>
> It must be added to docs of ANTLR
The information is around and I seem to repeat this concept a lot on
the list that you can set k to what you want but ANTLR uses the minimum
needed <= k. JavaCC for example forces you to specify the lookahead to
use per decision (if k>1 I believe); antlr does some groovy analysis
etc... to relieve you of this. Most tools force k=1 since they can't
do lookahead computation at all let alone do the nondeterminism
analysis. :)
Ter
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