Matthew Pocock wrote:
Hi,
I've been working a lot with maps, sets and lists. While the process of
getting things out of them is abstracted by foldable, traversable and
friends, the process of building one up is not. Would it be possible to have
something like:
class Buildable b where
empty :: b a --makes an empty b with elements of type a
insert :: a -> b a -> b a --inserts the new element into the buildable
Another approach uses :
singleton :: a -> b a
and then just
mappend :: b a -> b a -> b a
i.e. make b a into a Monoid.
singleton = pure = return, if there happens to be a Monad/Applicative
instance around.
And indeed there *will* be a Monad, if there is a sensible way of
defining concat :: b (b a) -> b a, which there probably is.
Jules
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