Jake McArthur wrote:
Andrew Coppin wrote:
But on the other hand, that would seem to imply that every monad is
trivially applicative, yet studying the libraries this is not the case.
Actually, it is the case. It is technically possible to write:
instance Monad m => Applicative m where
pure = return
(<*>) = ap
We don't include the above definition because it elimimates all
possibility of specialization.
I don't follow.
The reason for the separation of the two for many functions is so that
types which are instances of only one of the two can still take
advantage of the functionality.
Well, that makes sense once you assume two seperate, unconnected
classes. I'm still fuzzy on that first point though.
Foldable seems simplish, except that it refers to some odd "monoid"
class that looks suspiciously like "MonadPlus" but isn't... wuh?
A Monoid is simply anything that has an identity element (mempty) and
an associative binary operation (mappend). It is not necessary for a
complete instance of Foldable.
Again, it looks like MonadPlus == Monad + Monoid, except all the method
names are different. Why do we have this confusing duplication?
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