The report says explicit that instance declarations like instance C (a,a) where ..., or for (Int,a) or for [[a]] are not allowed. I tried to understand this by thinking these types are too complex, but I had to learn that a type may also be too simple, i.e. just writing instance D a is not allowed either. I had to look at the grammar to believe it. At least with a context as in the subject line, this should be useful. However, I don't suggest (only) this should be added, I rather hope that the people arguing for multi parameter type classes will make it (if not in Standard Haskell, then maybe in Curry:). I now only would like to know why this design decission was made, are there any problems with the instance declarations I have in mind? Christian Sievers
