The problem is that constrFields is not included with 6.2.1. You would need to build GHC from CVS. It will be in 6.4 for sure. And yes, you are right, there is no other way to get the names of all fields of a constructor. Ralf Stefan Reich wrote:

In recent versions of the GHC libraries, constrFields (as defined here http://www.cs.vu.nl/boilerplate/library/Data.Generics.Basics.html) has disappeared. I failed to figure out another way to get the names of all fields of a constructor.

Have I overlooked anything? Do I have to use Template Haskell?

-Stefan

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