Re: [Haskell-cafe] class default method proposal

On Dec 11, 2007 3:19 PM, David Menendez wrote:

On Dec 11, 2007 9:20 AM, Duncan Coutts wrote:

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So my suggestion is that we let classes declare default implementations of methods from super-classes.

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Does this proposal have any unintended consequences? I'm not sure. Please discuss :-)

It creates ambiguity if two classes declare defaults for a common superclass.

My standard example involves Functor, Monad, and Comonad. Both Monad and Comonad could provide a default implementation for fmap. But let's say I have a type which is both a Monad and a Comonad: which default implementation gets used?

Isn't a type which is both a Monad and a Comonad just Identity? (I'm actually not sure, I'm just conjecting) Luke