Manifold is an amazing piece of technology. It grew out of the "open type system" of Gosu: https://guidewiredevelopment.wordpress.com/2010/11/18/gosus-secret-

Manifold is an amazing piece of technology. It grew out of the "open type system" of Gosu: https://guidewiredevelopment.wordpress.com/2010/11/18/gosus-secret-sauce-the-open-type-system/ https://guidewiredevelopment.wordpress.com/2010/11/18/gosus-... The open type system was a simple API for adding new types to Gosu, allowing you to surface non-native types in a type safe way. A really nice way to do metaprogramming for a statically typed languge. Unfortunately Gosu never really went anywhere as an open source langauge, and Scott moved on to exploring javac plugins that let you accomplish the same thing in java. Amazing stuff.