The parallel typeclass pattern
Note
The Parallel typeclass is an abstraction over the conversion between an Applicative and a Monad, e.g. when we want to do certain operations in parallel with an applicative instance, but then convert back to the monad to use a for comprehension.
An example of it would be a conversion between Validated and Either, e.g. an Either with a List of errors as the Left. Another example is IO and ParIO.
The definition is as follows:
trait Parallel[F[_]] {
type M[_]
def F: Monad[F]
def M: Applicative[F]
def parallel: F ~> M
def sequential: M ~> F
}
parallel and sequential are natural transformations between the Monad and the Applicative, e.g. functions without loss of information.
