Shriram Krishnamurthi, Matthias Felleisen, Daniel P. FriedmanEuropean Conference on Object-Oriented Programming, 1998AbstractMany problems require recursively specified types of data and a collection of tools that operate on those data. Over time, these problems evolve so that the programmer must extend the toolkit or extend the types and adjust the existing tools accordingly. Ideally, this should be done without modifying existing code. Unfortunately, the prevailing program design strategie...