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]> 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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