This document provides an overview of the Clojure and Scala programming languages. Clojure is a Lisp dialect that runs on the JVM and was created in 2007 by Rich Hickey. It emphasizes immutability and functional programming. Scala is a multi-paradigm language that runs on the JVM and was created in 2004, based on Haskell. It is statically typed and supports both object-oriented and functional programming. Both languages can be used for web development, with Clojure using Compojure/Ring and Scala using SBT as their build systems. Examples of core functions like map, filter, and reduce are provided for each language.

1. Clojure / Scala
Diego Pacheco

3. Clojure
❏ 2007
❏ Rich Hickey
❏ JVM based but also CLR and JavaScript
❏ Functional dialect of Lisp
❏ Immutability & Immutable Data Structures
❏ Great interoperability with Java
❏ But -> Slow and Hard to troubleshoot.

4. Who is using Clojure?
https://clojure.org/community/companies

7. “Function as Data, Data as
functions” -- RH.
You don't need classes: Just Functions and Data!

9. Lisp

10. Lisp

12. Getting started with lien (Clojure build system)
❏ Clojure Build System
❏ Compatible with Maven Repos
❏ Super Easy to use https://leiningen.org/

13. Hello World on lein REPL

14. From a File (*.clj)

15. From a File (*.clj)

16. From a File (*.clj)

17. Basics
❏ Lists ()
❏ Vectors []
❏ Assign with Let
❏ “Strings”
❏ seq
❏ if

18. Functions

19. reduce

20. reduce

21. map

22. map

23. filter

24. filter

25. every?

26. Pipeline Operator (->>)

27. Sets
❏ Like Math Sets
❏ Unsorted
❏ NO Duplicates
❏ Efficient:
❏ Checking
❏ Removal
❏ (sorted-set)

28. SortedSets

29. Maps
❏ Also known as
❏ Dictionaries
❏ Hash Maps
❏ Assoc k/v pairs
❏ Domain data
❏ (sorted-map)

30. Working with “Pojos” == Maps.
❏ What can you do with a
Pojo in OOP? Nothing.
❏ In clojure? A lot !!!
❏ Remember “Alan Perlis”
❏ No need to define “schema”
❏ Productivity
❏ Simplicity

31. defrecord here is our class be happy :-)

32. https://github.com/clojure/core.match
Clojure also has Pattern Matcher

33. Web Development ... Compojure & Ring
$ lein new compojure hello-world
$ cd hello-world
$ lein run server-headless

34. Open your browser on http://localhost:3000/

35. handler.clj

36. https://clojuredocs.org/

37. Exercises
1. Write a function which returns the last element in a sequence without using *last*.
Test data: (A) [10 20 30 40 50] (B) '(10 8 1) (C) ["x" "y" "z"]
2. Write a function which sum of a sequence of numbers without using *reduce*.
Test data: (A) [1 2 3 4 5 6] (B) '(0 0 -1 1 2 3) (C) #{40 50 25 15 10}
3. Write a REST service with clojure, all persistence needs to be done in memory using maps or records.
You will need to create an BANK application with: deposit, withdrawal, check balance, transfer
money into other accounts. You will need do proper validations and also unit tests. Your application
need to use lein and compojure there are no other frameworks/libs allowed.
You cannot use: for, if and let.

38. Scala
❏ 2004
❏ Functional Programing Language
❏ Based on Haskell
❏ Runs on the JVM also JavaScript
❏ Statically typed
❏ Better Java
❏ Awesome for Big Data / ML
❏ Created by Martin Odersky

39. SBT
❏ Build System for Scala
❏ IF you are working with scala you also
could do:
❏ Maven
❏ Gradle
❏ In practice SBT is the right choice.

40. Helloworld Scala + SBT

41. Helloworld Scala + SBT

42. SBT has a REPL too ($ sbt console)

43. Functions
❏ Functions
❏ Lambdas
❏ Are all Objects
❏ Since
implementation in
java (JVM).

44. Partial Application
❏ Partial
❏ Lazy
❏ Composition
❏ Re-use

45. Partial Application via Currying
❏ Partial
❏ Lazy
❏ Composition
❏ Re-use

46. Variable lengths arguments or in java terms varargs.
❏ *
❏ Dynamic
❏ Generic
❏ Similar to
java

47. OOP in Scala: Class
❏ Scala support OOP
❏ Here is the better
java part starts
❏ Simple
❏ Clean
❏ Less Verbose

48. OOP in Scala: Class Constructor + String Interpolation

49. OOP in Scala: Inheritance
❏ Class Hierarchy
❏ Polymorphism

50. OOP in Scala: Polymorphism Overriding
❏ Class Hierarchy
❏ Polymorphism
❏ Overriding

51. OOP in Scala: Traits
❏ Similar to Java Interfaces
❏ However you can have code
❏ Fundamental part of type
system (“Algebra”)
❏ One of best things in Scala
❏ Be Careful it can get crazy :D
❏ Stay practical stay clean!

52. OOP in Scala: Generics + Types
❏ Generics
❏ Types
❏ Abstractions
❏ Leverage
Compiler
❏ Haskell way

53. Apply
❏ Apply
❏ Code runs
❏ Default in Scala
❏ Like toString
In Java but better
❏ Super useful

54. OOP in Scala: Objects
❏ Different then Java Objects
❏ Objects are single instance
❏ It's how you do Singletons in Scala
❏ Great for org static functions
❏ Often classes have companion Objects
in Scala.
❏ Functions in Scala are Objects.

55. Pattern Matcher
❏ One of the best features
In Scala Language.
❏ Support ifs
❏ Support “_”
❏ Support type matching
❏ Better than Switch

56. Pattern Matcher

57. Case classes
❏ One of the best features
In Scala Language.
❏ Super charged Classes
❏ Equality & toString
Support
❏ Work on Pattern
Matcher
❏ Super clean syntax

58. Collections
❏ Like in Java
❏ But much better
❏ Immutable
❏ Mutable
❏ Tupes
❏ Sets, Arrays, Lists,
❏ Maps vs Map

59. map, filter, foldLeft
❏ Functional
Combinators
❏ Core FP prog
❏ Super useful
❏ Day by Day work

60. Exercises
1. Write a function which finds the last element in a List without using *last*.
Test data: (A) List(1,2,3,4,5,6,7,8) (B) List(“1”,”2”,”3”) (C) List(1.0,2.0,3.0)
2. Write a function which Flatten a nested list structure.
Test data: (A) flatten(List(List(1, 1), 2, List(3, List(5, 8)))) (B) (List(), 2, List(3,4))
3. Write a REST service with Scala, all persistence needs to be done in memory using maps or records.
You will need to create an BANK application with: deposit, withdrawal, check balance, transfer
money into other accounts. You will need do proper validations and also unit tests. Your application
need to use lein and compojure there are no other frameworks/libs allowed.
You cannot use: for, if and let.

61. Clojure / Scala
Diego Pacheco