Band

Band instances must satisfy scalaz.Semigroup.SemigroupLaw and 1 additional law:

• '''idempotency''': forall a. append(a, a) == a

A semigroup in type F must satisfy two laws:

• '''closure''': ∀ a, b in F, append(a, b) is also in F. This is enforced by the type system.
• '''associativity''': ∀ a, b, c in F, the equation append(append(a, b), c) = append(a, append(b , c)) holds.

The default definition exploits idempotency to optimise to O(1)

The binary operation to combine f1 and f2.

Implementations should not evaluate the by-name parameter f2 if result can be determined by f1.

An scalaz.Apply, that implements ap with append. Note that the type parameter α in Apply[λ[α => F]] is discarded; it is a phantom type. As such, the functor cannot support scalaz.Bind.

Every Semigroup gives rise to a scalaz.Compose, for which the type parameters are phantoms.