Simon Peyton Jones asked

What's going on here? No other library module defines this function, except in Cabal! Simon

That was my fault; I'm very sorry. I had added that function (similar to Data.List.dropWhileEnd, but not the same) to compiler/utils/Util.lhs and to another module that used it, and then forgot it was not available in libraries/base/GHC/. Since neither Phab nor I run Windows, there was little hope of catching the mistake before it went out. I believe Joachim Breitner has fixed the problem now by using Data.List.dropWhileEnd to construct that error message—the difference in behavior doesn't matter there. David Feuer