Ok, sorry for the spam, accidentaly hit the send button =/.
On Wed, Dec 14, 2011 at 11:03 PM, Felipe Almeida Lessa
<felipe.le...@gmail.com> wrote:
> On Wed, Dec 14, 2011 at 4:09 PM, James Cook <mo...@deepbondi.net> wrote:
>> So a case could be made that, just as "forever (Just 1)" being nonsensical
>> doesn't invalidate "instance Monad Maybe", "some (Just 1)" being nonsensical
>> doesn't invalidate "instance Alternative Maybe". And on the other hand, a
>> case could be made that the importance of "some" and "many" justifies the
>> creation of a subclass of Alternative where they actually are mandated to be
>> meaningful rather than just definable.
Being in the same typeclass means that you can define
instance Alternative Maybe where
...
some Nothing = Nothing
some (Just _) = error "Alternative.some: used with Just (loops forever)"
many Nothing = Nothing
many (Just _) = error "Alternative.many: used with Just (loops forever)"
Cheers,
--
Felipe.
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