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

FUNCTIONAL GROOVY, ARE YOU KIDDING ME?

GROOVY IS NOT HASKELL RUSSEL WINDER

* have a look at https://github.com/frege/frege

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

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

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

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

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

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

ITERATORS (1)

ITERATORS (2) p

ITERATORS

GEEKS & BEERS

Functional Java Lambdaj

Google Guava

Johan Mattias

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

USE CASE 1 Find the cheapest beer

USE CASE 2 Find the most expensive beer

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

USE CASE 4 Get all the beer names

USE CASE 5 What’s the total price

PROS & CONS Java collections Closures! Plays nice with all other functional frameworks Metaprogramming!

Non-lazy evaluation Streams not included in core filter/map/reduce

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

STREAMS (1) Lazy generators. Extension module created by @tim_yates

http://timyates.github.com/groovy-stream/

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

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

STREAMS (JDK8) Collection and Lambda friendly, lazy evaluation

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

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

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

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

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

MEMOIZATION Cache computed values for increased performance

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

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

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

IMMUTABILITY The @Immutable AST transformation makes writing immutable classes trivial

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

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

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

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

THANK YOU!

HTTP://PEOPLE.CANOO.COM/SHARE

Andres Almiray Ix-chel Ruiz

@aalmiray @ixchelruiz