09 Oct 2001 13:55:04 -0700, Carl R. Witty <cwitty@newtonlabs.com> pisze:

The TREX paper from Mark Jones and Benedict Gaster (I hope I have the names right) had both extensible records and extensible variants (extensible variants being what you would need to implement downcasts),

I don't think so. Here is how the requirement can be formulated: We need some type T such that it's possible to define a family of functions for arbitrary choices of A: upA :: A -> T downA :: T -> Maybe A satisfying downA (upA a) = Just a. We want to choose the type for T before deciding the exact set of types for A. -- __("< Marcin Kowalczyk * qrczak@knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK