sashite-ggn

https://github.com/sashite/ggn.rb

A pure functional Ruby implementation of the General Gameplay Notation (GGN) specification v1.0.0. Provides a movement possibility oracle for evaluating pseudo-legal moves in abstract strategy board games. Features include hierarchical move navigation (piece → source → destination → transitions), pre-condition evaluation (must/deny), and state transition support via STN format. Works with Chess, Shogi, Xiangqi, and custom variants.