September 2018
Intermediate to advanced
398 pages
9h 43m
English
Content preview from Scala Programming Projects
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Laws
As you would expect, Applicative must conform to some laws.
Given a type F that has an Applicative[F] instance, for all types A given an instance fa: F[A], the following equalities must be verified:
- The Applicative identity is as follows:
((identity[A] _).pure[F] <*> fa) == fa
When we put the identity function in a F context using pure and call <*> on fa, it does not change fa. It is similar to the identity law in Functor.
- The Applicative composition, given the instances fab: F[A => B] and fbc: F[B => C], is as follows:
(fbc <*> (fab <*> fa)) == ((fbc.map(_.compose[A] _) <*> fab) <*> fa)
It is similar to the composition preservation in Functor . By using compose, we can change the parenthesis around the <*> expressions without changing ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.