1.
Presented By: Girish Chandra Bharti (Module Lead Software
Consultant @ Knoldus)

2.
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3.
Agenda

4.
Introduction to monix
● Monix is a high-performance Scala / Scala.js library
for composing asynchronous, event-based
programs.
● A Typelevel project, Monix exemplifies pure,
typeful, functional programming in Scala, while
making no compromise on performance.

5.
Major highlights in Monix
● Exposes the kick-ass Observable, Iterant, Task
and Coeval data types, along with all the
support they need
● Modular, only use what you need
● Designed for true asynchronicity, running on
both the JVM and Scala.js
● Excellent test coverage, code quality and API
documentation as a primary project policy

6.
Major highlights in Monix
● The project started as a proper implementation of
ReactiveX, with stronger functional programming
influences and designed from the ground up for
back-pressure.
● Made to cleanly interact with Scala’s standard
library compatible and out-of-the-box with the
Reactive Streams protocol.
● It then expanded to include abstractions for
suspending side effects and for resource handling.

7.
Monix Sub-projects
Sub-projects:
● monix-eval
● monix-execution
● monix-catnap
● monix-reactive
● monix-tail

8.
Monix Sub-projects
monix-eval:
Exposes the Task and Coeval data types,
for dealing with purely functional effects
in a principled way:
● Coeval
● Task

9.
Monix Sub-projects
monix-execution:
Provides low level utilities for dealing with
concurrency, exposing the JVM’s primitives and
building on top of the scala.concurrent package.
● Scheduler
● Cancelable
● Callback
● Future Utils
● Atomic
● Local

10.
Monix Sub-projects
monix-catnap:
Provide generic, purely functional utilities for
managing concurrency, building on top of the
Cats-Effect type classes:
● Circuit Breaker
● MVar

11.
Monix Sub-projects
monix-reactive:
Exposes the Observable data type, along with
adjacent utilities, a high performance streaming
abstraction that’s an idiomatic implementation of
ReactiveX for Scala:
● Observable
● Observers and Subscribers
● Consumer

12.
Monix Sub-projects
monix-tail:
The monix-tail sub-projects exposes Iterant, a
generic, purely functional, principled,
pull-based streaming data type:

13.
Companies that use Monix in production
● Abacus
● Agoda
● commercetools
● Coya
● E.ON Connecting Energies
● eBay Inc.
● Eloquentix
● Hypefactors
● Iterators
● Sony Electronics
● Zalando

14.
What is monix Coeval?
Coeval is a data type for controlling
synchronous, possibly lazy evaluation, useful
for describing lazy expressions and for
controlling side-effects.

15.
What is monix Coeval?
A visual representation of where Coeval sits in the design space:

16.
What is monix Coeval?
In summary the Monix Coeval:
● Works only for immediate, synchronous evaluation
● Can be a replacement for lazy val and by-name parameters
● Doesn’t trigger the execution, or any effects until value or run
● Allows for controlling of side-effects handles errors

17.
So what problems are we solving?
● lazy val cannot be expressed by developers as a type, you cannot
take a lazy val parameter or return a lazy val from a function.
def fun(lazy number): lazy [Int] = lazy val a = 10 (?????)
● by-name parameters, being just syntactic sugar that the compiler
understand, but a proper type isn’t properly exposed by Scala.

18.
So what problems are we solving?
● Scala has @tailrec as a compiler workaround to the JVM not
supporting tail-calls elimination, but it does not work for mutually
tail recursive calls and thus limited.
● The scala.util.Try type is overlapping in scope, given the Coeval
focus on error handling, but doesn’t have lazy behavior.

19.
Monix Coeval evaluation
To evaluate a Coeval instance you can invoke its value command:

20.
Monix Coeval
As Try Implementation:

21.
Monix Coeval
Coeval to Task:

22.
Monix Coeval
Tail Recursion:

23.
Monix Coeval Builders
● now
● eval
● evalOnce
● defer
● raiseError
● unit

24.
Monix Coeval
Memoization:

25.
Monix Coeval
FlatMap:

26.
Monix Coeval
Restart:

27.
Monix Coeval
Resource Clean up:

28.
Monix Coeval
Error Handling:

29.
Q & A

30.
References
● https://monix.io/docs/current/eval/coeval.html
● https://monix.io/
● https://monix.io/docs/current/