brbrown25/learn-fp

learn-by-doing course/tutorial for functional programming on scala

Learn Functional Programming course/tutorial on Scala

Intro

This course/tutorial was created with purpose to better understand functional programming idioms using Scala language. It covers type classes, monoids, functors, applicatives, monads, traversable/foldable, monad transformers, free monad.
Material is structured as set of stub/unimplemented functions/classes and tests for them. Your objective is to make all unit tests green. It is learn-by-doing course.

Example session

Inspiration

NICTA course was a great and interesting challenge for me to do in Haskell. I think Scala community will benefit from the similar course.

Target audience

The material in here is quite poor on theoretical/explanation part. I have tried to link material from other authors that I have found to be good into this course Readme to compensate for this. Some prior experience with functional idioms is recommended, but not necessary.

How to start

Just git clone this repository and follow steps in progression section. You can use any IDE and verify your results using sbt test. For me intellij works best - you can easily run individual tests out of it. In case if you got stuck - check answers branch.

Progression

It is important to keep the progression - a lot of things depend on each other. Implementing something = making all tests green for that thing.

Type classes

• Observe general type class pattern in learnfp/typeclass/TypeClass.scala.
• Implement learnfp/typeclass/TotalOrder.scala
• Implement learnfp/typeclass/Show.scala
• Implement learnfp/typeclass/Eq.scala
• Extra material:
  • https://blog.scalac.io/2017/04/19/typeclasses-in-scala.html

Monoids

• Observe general monoid pattern in learnfp/monoid/Monoid.scala
• Implement learn-fp/src/main/scala/learnfp/monoid/ListMonoid.scala
• Implement learn-fp/src/main/scala/learnfp/monoid/SimpleMonoid.scala
• Implement learnfp/monoid/PairAdditiveMonoid.scala
• Extra material:
  • Bartosz Milewski: Category Theory 3.1: Examples of categories, orders, monoids

Functors

• Observe general functor pattern in learnfp/functor/Functor.scala
• Implement learnfp/functor/Id.scala
• Implement learnfp/functor/Maybe.scala
• Implement learnfp/functor/List.scala
• Implement learnfp/functor/Disjunction.scala
• Implement learnfp/functor/Writer.scala
• Implement learnfp/functor/State.scala
• Extra material:
  • http://learnyouahaskell.com/functors-applicative-functors-and-monoids
  • https://thedet.wordpress.com/2012/04/28/functors-monads-applicatives-can-be-so-simple/
  • Bartosz Milewski: Category Theory 6.1: Functors

Monads

• Observe general monad pattern in learnfp/monad/Monad.scala
• Implement learnfp/monad/Id.scala
• Implement learnfp/monad/Maybe.scala
• Implement learnfp/monad/List.scala
• Implement learnfp/monad/Disjunction.scala
• Implement learnfp/monad/Writer.scala
• Implement learnfp/monad/State.scala
• Extra material
  • Brian Beckman: Don't fear the Monad
  • http://eed3si9n.com/learning-scalaz/Monad+transformers.html

Foldable

• Implement foldable in learnfp/foldable/Foldable.scala

Applicatives

• Observe general applicative pattern in learnfp/applicative/Applicative.scala
• Implement learnfp/applicative/Id.scala
• Implement learnfp/applicative/Maybe.scala
• Implement learnfp/applicative/List.scala
• Implement learnfp/applicative/Disjunction.scala
• Implement learnfp/applicative/Writer.scala
• Implement learnfp/applicative/State.scala
• Extra material
  • https://en.wikibooks.org/wiki/Haskell/Applicative_functors
  • http://eed3si9n.com/learning-scalaz/Applicative.html

Traversable

• Implement learnfp/traversable/Traversable.scala

Nested

• Implement learnfp/nested/Nested.scala

IO

• Implement learnfp/io/IO.scala

Monad Transformers

• Observe general monad transformer typeclass in learnfp/transformer/MonadTransformer.scala
• Implement learnfp/transformer/IdT.scala
• Implement learnfp/transformer/MaybeT.scala
• Implement learnfp/transformer/WriterT.scala
• Implement learnfp/transformer/StateT.scala
• Extra material:
  • http://eed3si9n.com/learning-scalaz/Monad+transformers.html

Free monad

• Implement learnfp/free/Free.scala and pass all unit tests in learn-fp/src/test/scala/learnfp/free/FreeTest.scala
• Extra material:
  • http://blog.krobinson.me/posts/monads-part-2-the-free-monad/
  • https://underscore.io/blog/posts/2015/04/14/free-monads-are-simple.html

Contravariant functor

• Observe general contravariant functor pattern in learnfp/contravariant/ContravariantFunctor.scala
• Implement learnfp/contravariant/Show.scala
• Implement learnfp/contravariant/Predicate.scala

CoMonads

• Observe general comonad pattern in learnfp/comonad/CoMonad.scala
• Implement learnfp/comonad/Id.scala
• Implement learnfp/comonad/Env.scala

Bonus

• Implement Reader functor, monad, applicative and write unit tests for that
• Implement ReaderT and write unit tests for that
• Implement applicative for monad transformers
• Implement applicative for Free

What was left out

• Reader/ReaderT
• Eff

Bugs/Issues

In case if find a bug/issue - please report it to https://github.com/dehun/learn-fp/issues or e-mail me on yuriy.netesov@gmail.com
You also are very welcome to create PR.

Credits

• Yuriy Netesov - initial implementation
• Extra material references are owned by other authors