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PostgreSQL has a wonderful feature which is called User-Defined types. It allows anyone to create a new datatype, along with the relevant operators, which are then managed almost natively by Postgres.

I decided to use this feature to manage chessboard positions in a more efficient manner than the usual ASCII storage which looks like “rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR”

I named this new type EPD, for “Extended Position Description”. I know that all the relevant data is not present (I shall typically store information like the active color, the casting availability, and a few other fields), but it didn’t sound like a bad choice for a name.

It allows to do some cool things like:

– Create a table with the epd type

chess=# CREATE TEMPORARY TABLE test_epd(my_epd epd);
CREATE TABLE

– Insert a string - it gets automatically converted to a native format and only takes 32 bytes
chess=# INSERT INTO test_epd VALUES (’rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR’);
INSERT 0 1

– And converted back into a string

chess=# SELECT * FROM test_epd;
my_epd
———————————————
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR
(1 row)

– What’s on A2 ?
chess=# SELECT epd_piece_at(my_epd, ‘a2′) FROM test_epd;
epd_piece_at
————–
n
(1 row)

chess=#

The code is available here. The installation process is:

1. Compile: make
2. Install the .so: make install
3. Configure postgresql: cat epd.sql | psql