1. GETTING
FUNKY
WITH
ANDRES ALMIRAY IX-CHEL RUIZ
@AALMIRAY @IXCHELRUIZ

5. FUNCTIONAL
GROOVY,
ARE YOU
KIDDING ME?

6. GROOVY IS NOT
HASKELL
RUSSEL WINDER
* have a look at https://github.com/frege/frege

7. CLOSURES == FUNCTIONS
Closures are functions (i.e, blocks of code) with an
environment containing a binding for all free variables of the
function

8. CLOSURES == FUNCTIONS
Closures are NOT side effect free by design

9. CLOSURES: PARAMETERS (1)
Parameter types may be omitted if type information is not
needed

10. CLOSURES: PARAMETERS (2)
Parameters may have default values
NOTE: Default values must be defined from right to left

11. CLOSURES: DEFAULT
PARAMETER
Closures may have a default parameter named it

12. CLOSURES LEAD TO …
Iterators
Streams
Partial Evaluation
Composition
Memoization
Tail calls

13. ITERATORS (1)

14. ITERATORS (2)
p

15. ITERATORS

16. GEEKS & BEERS
Mattias Johan
Functional Java
Lambdaj
Google Guava

17. USE CASES
Given a list of beers and their prices:
• Find the cheapest beer
• Find the most expensive beer
• What’s the name of the most expensive beer
• Get all the beer names
• What’s the total price

18. USE CASE 1
Find the cheapest beer

19. USE CASE 2
Find the most expensive beer

20. USE CASE 3
What’s the name of the most expensive beer

21. USE CASE 4
Get all the beer names

22. USE CASE 5
What’s the total price

23. PROS & CONS
Java collections
Closures!
Plays nice with all
other functional
frameworks
Metaprogramming!
Non-lazy evaluation
Streams not
included in core
filter/map/reduce

24. S/COLLECT/MAP/
Don’t like collect? Use Groovy’s metaprogramming

25. STREAMS (1)
Lazy generators. Extension module created by @tim_yates
http://timyates.github.com/groovy-stream/

26. STREAMS (2)
Groovy is Java friendly. Use any Java library such as
functional-java

27. FJ MODULE EXTENSION
https://github.com/mperry/functionalgroovy
Update: Mark has posted some notes at
http://mperry.github.io/2013/07/28/groovy-null-handling.html

28. STREAMS (JDK8)
Collection and Lambda friendly, lazy evaluation

29. PARTIAL EVALUATION (1)
Currying creates a new closure with fixed parameters, left to
right

30. PARTIAL EVALUATION (2)
Currying may be applied right to left too, even on an arbitrary
index

31. OBJECTS AS PARTIAL EVALS
Any class may implement the call() method, enabling implicit
evaluation

32. COMPOSITION (1)
Closures may be composed (left to right) using the >>
operator

33. COMPOSITION (2)
Closures may be composed (right to left) using the <<
operator

34. MEMOIZATION
Cache computed values for increased performance

35. TAIL CALLS (1)
Recursive closures may use Tail Calls thanks to trampoline()

36. TAIL CALLS (2)
Apply @TailRecursive on methods
https://github.com/jlink/tailrec/
now included in Groovy 2.3!

37. METHODS AS CLOSURES
Any method may be transformed to a Closure using the .&
operator

38. IMMUTABILITY
The @Immutable AST transformation makes writing
immutable classes trivial

39. GPARS
http://gpars.codehaus.org/
Concurrent collection processing
Composable asynchronous functions
Fork/Join abstraction
Actor programming model
Dataflow concurrency constructs
CSP
Agent - an thread-safe reference to mutable state

40. PARALLEL COLLECTIONS
Gpars enhances JDK/GDK collections with parallel execution
enabled versions

41. MONADS
https://github.com/dsrkoc/monadologie

42. RESOURCES
• http://pragprog.com/magazines/2013-01/using-memoization-
in-groovy
• http://www.ibm.com/developerworks/views/java/
libraryview.jsp?search_by=functional+thinking
• https://github.com/jlink/tailrec/
• http://timyates.github.com/groovy-stream
• http://www.jroller.com/vaclav
• http://gpars.codehaus.org
• http://www.slideshare.net/arturoherrero/functional-programming-
with-groovy

43. THANK YOU!
HTTP://PEOPLE.CANOO.COM/SHARE
Andres Almiray Ix-chel Ruiz
@aalmiray @ixchelruiz