[Haskell-cafe] Can subclass override its super-class' default
implementation of a function?
siki
gabor at karamaan.com
Mon Apr 27 17:00:18 EDT 2009
I'm not sure if this is possible at all. I'd like to do something like this:
class A a where
foo :: a -> Double
foo a = 5.0
class (A a) => B a where
foo a = 7.0
data Blah = Blah
data Bar = Bar
instance A Blah
instance B Bar
let blah = Blah
bar = Bar
foo blah -- should print out 5
foo bar -- should print out 7
Basically, I have a bunch of instances that have a common functionality but
I'd like to be able to group those instances and give each group a different
default implementation of that functionality. It's so easy to do this in
Java, for example, but I have no idea how to do it in Haskell. The above
example will not compile, btw.
Thanks a lot
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