Henning,
I have read in the History of Haskell, that originally 'seq' should be a method of a type class, that can be automatically derived by a 'deriving' clause. It was also mentioned that this clean solution was dropped because of particular experiences with developing a parser. However the arguments appeared to me, like these were problems of debugging.
If I understood it correctly, the problem was more general than just debugging. Every introduction of seq in a function could result in the requirement to also adapt the type signatures of calling functions. What wasn't understood by then is that making a seq a type-class method is not enough to recover parametricity, which was the goal. This is explained in a recent paper by Daniel Seidel and Janis Voigtlaender: Daniel Seidel and Janis Voigtlaender. Taming selective strictness. In Stefan Fischer, Erik Maehle, and Ruediger Reischuk, editors, INFORMATIK 2009 – Im Focus das Leben, Beitraege der 39. Jahrestagung der Gesellschaft fuer Informatik e.V. (GI), 28. September – 2. Oktober, in Luebeck, volume 154 of Lecture Notes in Informatics, pages 2916–2930. GI, 2009. http://www.iai.uni-bonn.de/~jv/atps09.pdf Cheers, Stefan