Brian Hulley wrote:
Hi,
Looking at some of the ideas in
http://www.haskell.org/haskellwiki/The_Other_Prelude , it struck me that
the class system at the moment suffers from the problem that as
hierarchies get 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.
The class aliases proposal lists several similar shortcomings of the
current class system.
http://repetae.net/john/recent/out/classalias.html
Perhaps there is some reason this can't be done?
Some random thoughts:
How one would write instances? Using your Monad class, does
instance Monad F where
return = ...
(>>=) = ...
automatically define an instance for Applicative?
If it does: What if there already is such an instance? Which one gets
used for (>>)? The user-defined one or the Monad default? Is separate
compilation still possible? (If there is no instance right now, one
might pop out in another module...)
If it does not: How can one define it, without copy-and-pasting the default?
Zun.
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