> I've perhaps been trying everyones patiences with my noobish CT > questions, but if you'll bear with me a little longer: I happened to > notice that there is in fact a Category class in Haskell base, in > Control.Category: > > quote: > -------- > class Category cat where > > A class for categories. id and (.) must form a monoid. > > Methods > > id :: cat a a
This says that 'cat' must be a type constructor with two type arguments. In an instance of this type, a and b will refer to objects of the category and cat a b to the morphisms. Integer is NOT a type constructor with two type arguments, so instance Category Integer makes no sense. [] is a type constructor with one type argument, not two, so instance Category [] makes no sense either. Can you make Either an instance of Category? Can you make (,) an instance of Category? Can you make (a copy of) -> an instance of Category a different way? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe