PL/SWI-Prolog

Use SWI-Prolog as a Procedural Language inside PostgreSQL!

Status

This is still a work in progress. It just barely works!

Installation

$ make
$ sudo make install

Note that PostgreSQL development utilities and header files are required.

Example

See the example.prolog file which contains the following predicate definition:

break_chars(String, Char) :-
        atom_chars(String, Chars),
        member(Char, Chars).

From psql shell as superuser:

create extension plswipl;
CREATE EXTENSION
salva=# create or replace function break_chars(text) returns setof text
            as $$"/home/salva/g/pg/plswipl/example.prolog"$$ language PLSWIPL;
CREATE FUNCTION
salva=# select break_chars('all the letters');
 break_chars
-------------
 a
 l
 l
  
 t
 h
 e
  
 l
 e
 t
 t
 e
 r
 s
(15 rows)

salva=# 

Todo

• Investigate how to convert data from/to the Prolog side correctly.

• Add support for more data types, specifically arrays and json(b?)

• Learn how memory handling works under Pg and take advantage of it (DONE!)

• Add support for SPI

• Add support for doing FDW in Prolog?

• Store Prolog modules inside the database.

• Add trusted version for non superusers.

• Learn how a procedural language interactuates with having more than one schema or changing the session user.

• Fix this alarm exceptions thing.

• Investigate higher level approaches to Prolog/SQL interaction.

• Investigate how to use Prolog to provide a Datalog (or similar) interface to Pg.

Focus

My aim is getting PL/SWI-Prolog to be a correct, flexible and powerful Procedural Language backend.

At this point, structured, flexible and clear code is the most important thing.

Resist to optimize if that means making the code more complex.

Collaborating

Collaborations welcome! Just fork the project and start submiting pull requests!

License

The PL/SWI-Prolog extension is distributed under the MIT license. See the LICENSE file.