The Game Description Language is declarative, not imperative. It defines the rules of a game, but not the process by which a program should apply those rules to produce facts. This has led to a wide variety of implementations of GDL interpreters, or engines, that handle this computation, with a wide range in their speed and accuracy across games.
A paper presented at the GIGA'13 conference by Yngvi Björnsson and Stephan Schiffel compared the performance of six such engines on 12 games. (To access the paper, select "proceedings" on the conference website and scroll to page 55.) To follow up on this experiment, and to test my own creations, I decided to write an open-source framework for this type of performance testing.