Lambda the Ultimate

The "scrap your boilerplate" approach to generic programming allows the programmer to generic functions that can traverse arbitrary data structures, and yet have type-specific cases. However, the approach requires all the type-specific cases to be supplied at once, when the function is defined: the function is closed. In contrast, Haskell's type classes support open, or extensible functions, that can be extended with new type-specific cases as new data types are defined. In this paper we show how to extend the scrap-your-boilerplate approach to support this open style. On the way we demonstrate the desirablility of abstraction over type classes, and the usefulness of recursive dictionaries.

If you haven't been paying attention, this is your chance to learn about the "scrap your boilerplate" approach to generic programming in Haskell. We mentioned and discussed the earlier papers in the series.

Like many of Peyton Jones's papers this one is an enlightening exploration of language design.