Herding CATS

book source: Scala with CATS

web source: herding cats

cats exercises: Scala Cats exercises

my study note: CatsStudyNote

Content

1. theory

2. herding cats

3. case studies

Note

Abstract implementations patterns

Functor: mapping

Applicative: zipping

Monad: sequencing

Traverse: iteration

Cats Typeclass cheat sheet

cheat sheet

1. Defining Signatures

Typeclass	Signature
Functor	F[A] => (A => B) => F[B]
Contravariant	F[A] => (B => A) => F[B]
Apply	F[A] => F[A => B] => F[B]
FlatMap	F[A] => (A => F[B]) => F[B]
CoFlatMap	F[A] => (F[A] => B) => F[B]
Traverse	F[A] => (A => G[B]) => G[F[B]]
Foldable	F[A] => (B, (B, A) => B) => B
SemigroupK	F[A] => F[A] => F[A]
Cartesian	F[A] => F[B] => F[(A, B)]

2. Derived Functions

Typeclass	Function	Signature
Functor	map fproduct as tupleLeft tupleRight void	F[A] => (A => B) => F[B] F[A] => (A => B) => F[(A, B)] F[A] => B => F[B] F[A] => B => F[(B, A)] F[A] => B => F[(A, B)] F[A] => F[Unit]
Contravariant	contramap	F[A] => (B => A) => F[B]
Apply	ap map2	F[A] => F[A => B] => F[B] F[A] => (F[B] => ((A, B) => C)) => F[C]
Applicative	ap unlessA whenA replicateA	F[A] => F[A => B] => F[B] F[A] => Boolean => F[Unit] F[A] => Boolean => F[Unit] F[A] => Int => F[List[A]]
FlatMap	flatMap followedBy forEffect mproduct flatten	F[A] => (A => F[B]) => F[B] F[A] => F[B] => F[B] F[A] => F[B] => F[A] F[A] => (A => F[B]) => F[(A, B)] F[F[A]] => F[A]
CoFlatMap	coflatMap coflatten	F[A] => (F[A] => B) => F[B] F[A] => F[A[A]]
Traverse	traverse mapWithIndex zipWithIndex sequence	F[A] => (A => G[B]) => G[F[B]] F[A] => ((A, Int) => B) => F[B] F[A] => F[(A, Int)] F[G[A]] => G[F[A]]
Foldable	foldLeft foldRight foldMap combineAll find exists forall toList isEmpty nonEmpty size	F[A] => (B => ((B, A) => B)) => B F[A] => (Eval[B] => ((A, Eval[B]) => Eval[B])) => Eval[B] F[A] => (A => B) => B F[A] => A F[A] => (A => Boolean) => Option[A] F[A] => (A => Boolean) => Boolean F[A] => (A => Boolean) => Boolean F[A] => List[A] F[A] => Boolean F[A] => Boolean F[A] => Int
SemigroupK	combine	F[A] => F[A] => F[A]
Cartesian	product	F[A] => F[B] => F[(A, B)]

Monad type class hierarchy

Cartesian            Functor
(product)             (map)
    |___________________|
              |
            Apply
            (ap)
     _________|_________
    |                   |
Applicative          FlatMap
  (pure)            (flatMap)
    |___________________|
              |
            Monad

Cats type class view:

thanks to tpolecat's project