Pure Functional Effects - from IO to ZIO

Effects in functional programming
From IO to ZIO
Effects in functional Programming - @justinhj (C)2019

Benefits of pure functions
Easy to reason about
Easy to combine
Easy to test
Easy to debug
Easy to parallelize

Benefits of pure functions
Easy to reason about
Easy to combine
Easy to test
Easy to debug
Easy to parallelize
Idemotency
Referential transparency
Memoization
Flexible evaluation

1. Total
Pure functions are

Functions that are not total

Total functions A -> B return a valid B for every A

Exceptions are not valid type B

Exceptions are not valid type B
Lost ability to compose

1.Total
2.Deterministic
Pure functions are

Pure functions are deterministic

Each A passed to whatDoIDo returns a different B for every call

Harder to reason about

Harder to test

1.Total
2.Deterministic
3.Without side-effects
Pure functions are

Functions that have side effects in the real world are not pure

Hard to test

Hard to test
Not referentially transparent

Hard to test
Not referentially transparent
Hard to compose

Anything you can’t “just” do twice is probably an effect
Effects

Pure functional programs are useless
Output to terminal
Get a record from a database
Updating a counter
Work with random numbers

Pure functional programs are useless
Output to terminal
Get a record from a database
Work with random numbers
Updating a counter

IO monads
Imperative Functional Programming [1993]
https://www.microsoft.com/en-us/research/wp-content/uploads/1993/01/imperative.pdf
P. Wadler and S.L. Peyton-Jones

IO monads
hello is an effect and we can now do it twice
without breaking referential transparency

IO monads
Lift a pure A to IO[A]
flatMap or bind
sequences two effects together

Monads in Scala
Implemented as a type class
Achieves the same as in Haskell
pure = put an A in a Monad
flatMap = sequence two monads
B

IO Monad - Future
Future is not a Monad
Future execution is eager
http://justinhj.github.io/2018/05/05/hacker-news-api-4.html
Futures allow asynchronous effects
They have pure and bind (Future.success and Future.flatMap)

IO Monad - Future

IO Monad - Future
Future is not a Monad Future execution is eager
http://justinhj.github.io/2018/05/05/hacker-news-api-4.html

IO Monad - Scalaz
Runar Bjarnason
https://apocalisp.wordpress.com/2011/12/19/towards-an-effect-system-in-scala-part-2-io-monad/
Direct conversion from Haskell

IO Monad - Monix (2.x series)
Alex Nedelcuhttps://monix.io/docs/2x/eval/task.html#design-summary

IO Monad - Cats Effect
Monix Task, Scalaz IO/Task became Cats Effect
Includes cancelation, stack safe trampolining, parallel execution and a green
threads system (fibres),
Daniel Spiewak - The Making of an IO
https://www.youtube.com/watch?v=g_jP47HFpWA

IO Monad - Cats Effect

IO Monad - ZIO
http://degoes.net/articles/bifunctor-io
IO[A]
becomes
IO[E, A]

IO Monad - ZIO

IO Monad - ZIO
Brings errors to type level

IO Monad - ZIO
Brings errors to type level
More efficient than a EitherT

IO Monad - ZIO
ZIO[R,E,A]
http://degoes.net/articles/zio-environment

IO Monad - ZIO
Example ZIO program

IO Monad - ZIO
Sample environment module

IO Monad - ZIO
Test module

Thank you!
Questions?

Pure Functional Effects - from IO to ZIO

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