Erik Ernst, The expression problem, Scandinavian style. MASPEGHI 2004.

This paper explains how higher-order hierarchies can be used to handle the expression problem. The expression problem is concerned with extending both the set of data structures and the set of operations of a given abstract data type. A typical object-oriented design supports extending the set of data structures, and a typical functional design supports extending the set of operations, but it is hard to support both in a smooth manner. Higher-

order hierarchies is a feature of the highly unified, mixin-based, extension-oriented kind of inheritance which is available in the language gbeta, which is itself a language that was created by generalizing the language Beta.

MASPEGHI, in case you wonder, stands for *MechAnisms for SPEcialization, Generalization and inHerItance*. On the site you'll also find the presentation related to the paper. And oh, gbeta is here.

I wonder what the Scala guys have to say about all this...

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