typelevel
Should we remove the construction methods in algebra.lattice?
In the lattices, we have a number of methods to create ring structures from lattices. These seem like particular constructions to me, and perhaps not best bolted onto the traits themselves.
For instance, we could add:
trait Semigroup[T] {
//...
def asMonoid: Monoid[Option[T]]
}
which is a construction to create a Monoid from a semigroup using None as the unit, but I wouldn't want to do that. Similarly we can build a Ring[(BigInt, T)] from a Rng[T] by adding a 1 element and counting how many times it has been added (a: BigInt, t: T) = a * 1 + t, but again, that construction I would rather have a named class for that than bolt it onto the trait.
By contrast, .meetSemilattice is not a construction, it is exactly taking the meet and returning a Semilattice instance which combine == meet. This feels different to me.
Somewhat similarly is the .dual. Maybe we should have case class DualLattice[T](lattice: Lattice[A]) extends Lattice[A] or some such, instead of methods on the traits.
Note that the return type of dual is overridden in more specific lattices, so one DualLattice class will not cover them all.
Yeah. dual we can either set aside from this discussion, or make DualX for each X. I can't see another way to do that.
I would be fine removing these things. It may be the case that we will want to use something more like Dual[Bool, A] to do something like this.
Given all the confusion around these methods (what to call them, what their return types should be, whether they will be refined in subtypes, etc.) I think we should just remove them and handle this via a different mechanism.