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
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