I admit that I do not really know how to divide the rules, although I
believe I could deduce it from the context. I guess that Marpa would have
two places/methods to feed the BNF, one for the lexical and one for the
structural, so I have to read more and more carefully.
Thanks
ZA
On Thursday, December 4, 2014 1:06:48 PM UTC-5, Jeffrey Kegler wrote:
>
> A lot of standards BNF has been converted to Marpa, but doing it fully
> automatically is problematic, because standards BNF was written on the
> assumption that there is no practical way to parse directly from BNF, and
> the standards writers feel free to cut a corner or two.
>
> They do this in particular with the lexing/parsing boundary. As a
> practical matter, parsers almost always need a lexical layer and a
> structural layer, and in Marpa's SLIF, these have two different sets of
> rules, one using '::=", and the other using a tilde ('~'). To translate
> the standards BNF into Marpa's SLIF, you'll have to divide the rules into
> lexical (L0) and structural (G1).
>
> I am pretty sure there are (or at least have been) large Marpa-powered SQL
> subsets running out there, running in production environments, because of
> questions that have come in. But those are proprietary. And I am not
> aware of any open-source full SQL parser in Marpa.
>
> Guessing, converting the SQL BNF to Marpa is quite possible, but might
> take some time and effort, particularly if you're not already familar with
> BNF and the lexical/structural distinction in traditional parsing.
>
> On Thu, Dec 4, 2014 at 9:37 AM, Zeev Atlas <[email protected] <javascript:>
> > wrote:
>
>> Hi all
>> I am new to Marpa, so I may be trying to chew too much, but my question
>> is of general nature.
>> I am interested ultimately in parsing SQL (not running it, just parsing
>> into structures that I could than analyze.) So I wrote a simple program
>> that strip the SQL 2003 BNF file (http://savage.net.au/SQL/sql-2003-2.bnf)
>> from irrelevant data and try to feed it to Marpa as is.
>>
>> In the BNF I have clauses like this:
>> <percent> ::= %
>> which I already figured out I need to change to something like
>> <percent> ::= '%'
>>
>> My issue is the infamous clauses:
>>
>> <space> ::=
>> or worse
>> <quote> ::= '
>>
>> Could somebody tell me please how should I deal with those
>> note that
>> <space> ::= ' ' and <quote> ::= ''' or <quote> ::= '''' do not work
>>
>> BTW, if anybody already did a full featured (not specific dialect) SQL
>> parser (SQL::Statement is a relatively incomplete subset) or knows about
>> such one, please let me know. Also, I am looking for dialect specific full
>> BNF files if available
>>
>> Thanks all
>> ZA
>>
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