An introduction to Clojure at why you should take a closer look.

1. Clojure
Why does it matter?
@friemens

2. ● Published 2008 by Rich Hickey.
● Dynamically typed.
● Compiles to bytecode.
A pragmatic Lisp for the JVM

3. &
Simplicity
Advanced stuff
Lisp
Deconstruction

4. &
Simplicity
Advanced stuff
Lisp
Deconstruction

5. Few ubiquitous data
structures and
powerful core library.
Simple Complicated
Data encapsulated
behind specific APIs of
OO classes.
Immutable data. Mutable class
instances &
synchronization.
Embedded „code
generators“.
External DSL tooling.
Pure functions. Side effects &
dependence on
context.

6. Design is deconstruction
Small libraries,
no big frameworks!
HTTP
server
Middle-
ware
functions
Routing
function
Handler
functions
Page
renderer

7. Deconstructing the database
Datomic
A modular,
facts-based
database system.
Storage service
Transactor
Query
Cache
Peer library
Application
Database

8. State and Identity
OO style (conflated) Clojure style (separated)

9. &
Simplicity
Advanced stuff
Lisp
Deconstruction

10. &
Simplicity
Advanced stuff
Lisp
Deconstruction

11. Huh? Lisp?
Lisp!
Other Languages
Time
Expressive
Power

12. The elegance of Lisp

13. http://xkcd.com/297

14. Functional programming
Functions as values
Powerful data structures
„[...] a unit tester's wet dream.“
No assignments
Laziness

15. Example: Square root approximation
gn+1 := (n/gn + gn) / 2

16. Concise code
public <K,V> Map<V, K> revertKeysVals(Map<K, V> src) {
final Map<V, K> dst = new HashMap<V, K>();
for (Map.Entry<K, V> e : src.entrySet()) {
dst.put(e.getValue(), e.getKey());
}
return dst;
}
(defn revert-kv [m]
(->> m (map (juxt second first)) (into {})))

17. Prefer purity
Pure functions
Side effects
Context

18. Code is data, or: why does Lisp look different?
Code
Data

19. Common How it could be
Build
config
DSL
grammar
Settings
Serialization
XML
Xtext
.properties
JSON
Debug
output
Anything
EDN
EDN
EDN
EDN
EDN
Clojure is a superset of Extensible Data Notation

20. A powerful language allows for simpler tools

21. Interactive development
Demo

22. &
Simplicity
Advanced stuff
Lisp
Deconstruction

23. &
Simplicity
Advanced stuff
Lisp
Deconstruction

24. Persistent datastructures
0 1 2 3 4 5 6 6 7 8 9
10
7

25. Concurrency support
Actor style:
Pulsar librarySoftware
Transactional
Memory
CSP style:
core.async library
Widely used:
Synchronization and LockingJava
Clojure

26. Advanced libraries
core.logic
core.async
core.typed
core.reducers
Datomic
map + fold parallelized
Logic programming
CSP style programming
Optional type system
Facts-based database

27. Internal DSLs just happen
HTTP routing
UI form description
Data access

28. Full stack Clojure
Browser
App Server
Database
ClojureScript
Clojure
Datomic

29. &
Simplicity
Advanced stuff
Lisp
Deconstruction

30. Advanced thinking
Expressive power
Fosters dev skills
Advanced concurrency support
Perfect for unit testing
What's in for you?
Concise data manipulation
Interactive programming

31. Thank you. Questions?
@friemens www.itemis.de