At 2002-01-18 00:06, Cagdas Ozgenc wrote: >Why does Haskell let you write functions that are not a part of type class?
Well, what classes should such functions as const, id and (.) be members of? const :: a -> b -> a; const x y = x; id :: a -> a; id x = x; (.) :: (b -> c) -> (a -> b) -> (a -> c); (.) f g x = f (g x); >For example instead of > >elem :: Eq a => a -> [a] -> Bool >map :: (a -> b) -> [a] -> [b] > >class Container a where > elem :: Eq b => b -> a b -> Bool > map :: (b -> c) -> a b -> a c > >would define methods that can work on all containers, Actually this would only work on container type-constructors. If you had a type that was some kind of container only of Char, you could not make it an instance of your Container. >and create a discipline to write more reusable and generic functions. There's already a generalised version of map, called fmap, that works on any Functor type. Picking the correct generalisation is often not obvious... -- Ashley Yakeley, Seattle WA _______________________________________________ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
