One of the first functional data structures I reach for when writing
code that interacts with a person or another system is
Validation. It allows me to accumulate, parse, transform,
and verify input in a type-safe and parallelizable operation.
In this talk, we look at Validation: how to use it, why
it works, and where in category theory it comes from. We'll see how to
use the implementations provided by Scalaz and Cats, as well as how to
roll our own from scratch.