Lambda the Ultimate

The ECOOP 2012 best paper award this year was given to Bruno Oliveira and William Cook for the paper "Extensibility for the Masses: Practical Extensibility with Object Algebras".

This paper is (yet another) solution to the expression problem. The basic idea is that you create a family of objects via an Abstract Factory. You can add new objects to the family by extending the factory as per usual, but the twist is you can also add new operations by overriding the factory methods to do other things, like evaluation or pretty printing.

Bruno has also been collecting sample implementations using Object Algebras solving a simple expression problem example.