Modeling Game Mechanics With Ceptre

Game description languages have a variety of uses, including formal reasoning about the emergent consequences of a game's mechanics, implementation of artificial intelligence decision making where the game's rules make up the space of possible actions, automated game and level generation, and game prototyping for the sake of low-time-investment design and tinkering. However, in practice, a new game description language has been invented for almost every new use case, without providing formal underpinnings that follow generalizable principles and can be reasoned about separately from the specific software implementation of the language. Ceptre is a language that attempts to break this pattern, based on an old idea known as multiset rewriting. This article describes the language formally, through example, and in a tutorial style, then demonstrates its use for writing formal specifications of game mechanics so that they may be interactively explored, queried, and analyzed in a computational framework. Ceptre allows designers to step through executions, interact with the mechanics from the standpoint of a player, run random simulated playthroughs, collect and analyze data from said playthroughs, and formally verify mathematical properties of the mechanics, and it has been used in a number of research projects since its inception, for applications such as procedural narrative generation, formal game modeling, and game AI.