Bulat Ziganshin wrote:
Hello Brian,
Thursday, January 4, 2007, 10:00:05 PM, you wrote:
deeper, the programmer is burdened more and more by the need to cut-and-paste method definitions between instances because Haskell doesn't allow a superclass (or ancestor class) method default to be redefined in a subclass.
i've runned into this problem with Streams library. finally i've decided to wrote bodies of such methods outside of class: [example snipped]
Hello Bulat, Thanks for the workaround, which solves the need to copy and paste method bodies though not the problem of having to write out instance decls for a potentially large chain of classes leading to the subclass of interest. Part of the motivation for proposing that a superclass method default could be redefined in a subclass (or a particular instance) is that it would allow some refactorings of the class hierarchy without affecting code that just uses the subclass - in particular it would allow existing code using Monad to compile unchanged even when Monad moved down to Functor => Applicative => Monad because return and >>= are enough to get completely defined instances for Functor and Applicative. Best regards, Brian. -- http://www.metamilk.com