Diego Yanivello <[EMAIL PROTECTED]> wrote in article <[EMAIL PROTECTED]> in gmane.comp.lang.haskell.general: > ERROR "Test.hs":12 - Overlapping instances for class "B" > *** This instance : B () > *** Overlaps with : B a > *** Common instance : B () > > but I don't have an instance "A ()" from which haskell can infer an > instance "B ()". > can somebody explain me that it is happening here?
Unfortunately, contexts in instance definitions are not taken into account when checking for overlapping instances. That is, two instances are regarded as overlapping as long as their heads can be unified. -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig International Human Rights Day * 2003-12-10 * http://www.un.org/rights/ What if All Chemists Went on Strike? (science fiction) http://www.iupac.org/publications/ci/2003/2506/iw3_letters.html _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
