Nim Chess 4

(c) Stefan Salewski
Version 0.5, 08-SEP-2017

Nim Chess 4 is a simple chess game written from scratch in Nim language with a basic GTK3 GUI.

This is the fourth version. While the first release was basically a test for the low level Nim GTK3 bindings, and the second release added a transposition table based on tables module from Nim’s standard library, the third one uses a custom hash table. This restricts memory consumption drastically. Current version uses about 340 MB of RAM, so playing on older hardware is no problem any more. This fourth version now uses the high level, gobject-introspection based GTK3 API. Chess engine is still identical with the third one but may change later. The GUI is still blocking for a few seconds when the computer is making its move. I think that is not a too serious restriction for now — later I may add threading support or maybe run the engine as a separate process and using socket communication for GUI. Doing that is some work and not really interesting…​

Visual appearance

Properties

• written in Nim language

• basic GTK3 GUI using high level API

• only 1200 lines of code

• move generation is based on an old gnuchess idea

• core component is of course alpha-beta-prunning

• a transposition table is used to reuse old results

With a time limit of a few seconds per move computation is generally 7 ply deep full width, with additional full capture analyses (quiescence search). Special moves like chess offers or captures are now deep extended, which should further increase playing strength, but I have not really verified that. In endgame deep of 10 ply and more is archived — now even the most difficult endgame king vs king/bishop/knight is solved in few moves/seconds. And I have added a set based history to prevent engine from repeating old positions.

Of course an opening library would increase playing strength, but I do not enjoy playing against a database too much, so I do not really intend to add one.

The graphical user interface is very basic currently — we play with white pieces against computer. No undo, no hints. For next game we have to restart the program.

Maybe some day I will provide a more complete GUI. At least setting time limit and choosing side would be nice. That is really not much work, but not very interesting.

Parallel computing would be interesting too, but the engine is strong already, and of course parallel computing would increase power consumption, so maybe it is not that useful.

For this release we may need at least Nim v 0.17.1.

Install

For Linux:

First install gintro, the gobject-introspection based high level GTK3 bindings

https://github.com/StefanSalewski/gintro

And then

git clone https://github.com/stefansalewski/nim-chess4
cd nim-chess4
nim c -d:release board.nim

./board

The shipped nim.cfg file is this:

$ cat nim-chess3/nim.cfg
path:"$projectdir"
nimcache:"/tmp/$projectdir"
gcc.options.speed = "-march=native  -O3  -flto -fstrict-aliasing"

With gcc 6.3 this seems to generate the fastest executable with only 108 kB in size. You may try your own options — and maybe do first built without -d:release flag to check for bugs.

It may be possible to use it on Windows as well, for MacOSX installation seems to fail, as someone in Nim forum reported.

The older nim-chess releases 1 and 2 are still available at https://github.com/ngtk3 — I intend to delete them when this release is a bit more tested.