What is Cats library in Scala?
Answer
Cats (Category Theory Abstractions) is the most popular functional programming library for Scala, providing type class abstractions from category theory. Core type classes: Functor: map — transform values inside a context. Applicative: combine independent effectful values. Monad: flatMap — sequence dependent effectful computations. Foldable: fold structures. Traverse: sequence effects. Show: type-safe toString. Eq: type-safe equality. Semigroup/Monoid: combine values. Cats Effect: a separate library providing the IO monad for pure functional side-effect management and async programming. Cats provides Either utilities, Validated (accumulating errors), NonEmptyList, and much more. It is the foundation of many Scala ecosystems (http4s, Doobie, FS2). Understanding Cats is essential for senior-level Scala functional programming.
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