On Fri, Jul 05, 2019 at 07:55:15AM +0000, Tom Mercha wrote:
Dear Hackers
I am interested in implementing my own Domain Specific Language (DSL)
using PostgreSQL internals. Originally, the plan was not to use
PostgreSQL and I had developed a grammar and used ANTLRv4 for parser
work and general early development.
Initially, I was hoping for a scenario where I could have PostgreSQL's
parser to change grammar (e.g. SET parser_language=SQL vs. SET
parser_language=myDSL) in which case my ANTLRv4 project would override
the PostgreSQL parser module. I guess another direction that my project
could take is to extend PostgreSQL's SQL parser to factor in my DSL
keywords and requirements.
To make matters more complicated, this version of ANTLR does not
support code generation to C, but it does support generation to C++.
Integrating the generated C++ code requires making it friendly to
PostgreSQL e.g. using Plain Old Data Structures as described here
https://www.postgresql.org/docs/9.0/extend-cpp.html, which seems to be
suggesting to me that I may be using the wrong approach towards my
goal.
I would be grateful if anyone could provide any general advice or
pointers regarding my approach, for example regarding development
effort, so that the development with PostgreSQL internals can be smooth
and of a high quality. Maybe somebody has come across another DSL
attempt which used PostgreSQL and that I could follow as a reference?
I might be missing something, but it seems like you intend to replace
the SQL grammar we have with something else. It's not clear to me what
would be the point of doing that, and it definitely looks like a huge
amount of work - e.g. we don't have any support for switching between
two distinct grammars the way you envision, and just that alone seems
like a multi-year project. And if you don't have that capability, all
external tools kinda stop working. Good luck with running such database.
What I'd look at first is implementing the grammar as a procedural
language (think PL/pgSQL, pl/perl etc.) implementing whatever you expect
from your DSL. And it's not like you'd have to wrap everything in
functions, because we have anonymous DO blocks. So you could do:
DO LANGUAGE mydsl $$
... whatever my dsl allows ...
$$;
It's still a fair amount of code to implement this (both the PL handler
and the DSL implementation), but it's orders of magnitude simpler than
what you described.
See https://www.postgresql.org/docs/current/plhandler.html for details
about how to write a language handler.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
