1. From Python
to Scala
Sébastien Pierre, ffunction inc.
@Montréal Python, April 2010
www.ffctn.com
ffunction
inc.

2. Stuff I love about Python
●
Expressive (and compact)
●
Simple to learn
●
Lots of smartly designed libraries
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3. Stuff that I miss in Python
●
Closures (with syntax)
●
Easy concurrency (model and syntax)
●
… a compiler !!
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4. Scala - overview
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5. The language
●
JVM-based, compiled + « interpreted »
●
Functional + OO (post-functional)
●
~6 years old
●
used by Twitter, FourSquare
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6. The library
●
Anything in Java
●
Immutable types library (safe for concurrent apps)
●
Concurrency + actor model
●
Quality community-contributed libraries
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7. The feel
●
Make do with braces
●
map/filter/apply (and fold)
●
~25% more lines than with Python
●
Very good DSL-ability
●
Fast !
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8. Scala – basics
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9. Rich types
Scala Python
Array Array(1,2,3,4) (1,2,3,4]
Tuple (1,2,3,4) (1,2,3,4)
List List(1,2,3,4) (1,2,3,4)
Map Map(“a”>1, “b”>2) {“a”:1, “c”:2}
Set Set(1,2,3,4) set(1,2,3,4)
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10. Closures
[1,2,3] map { i => i + 1 }
{i:Int => i + 1 } # 1-param normal
(i:Int) => { i + 1 } # n-param normal
[1,2,3] map { _ + 1 } # implicit args
val f = { i:Int => i + 1}
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11. Classes + traits
class A
{…}
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12. Classes + traits
class A
{…}
class B
extends A
{…}
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13. Classes + traits
class A
{…}
class B
extends A trait T
with T {…}
{…}
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14. Classes + traits
class A trait U
{…} {…}
class B
trait T
extends A
extends U
with T
{…}
{…}
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15. Classes + traits
class A trait U
{…} {…}
class B
trait T
extends A
extends U
with T
{…}
{…}
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16. Batteries included
scala.xml.XML.load(
"http://ffunction.posterous.com/rss.xml"
) "item" "title" toList
List[scala.xml.Node] = List(<title xmlns:media="http://search.yahoo.com/mrss/"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:posterous="http://posterous.com/help/rss/1.0"
xmlns:atom="http://www.w3.org/2005/Atom">Notes on creating a multi­touch
interface</title>, <title xmlns:media="http://search.yahoo.com/mrss/"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:posterous="http://posterous.com/help/rss/1.0"
xmlns:atom="http://www.w3.org/2005/Atom">Formations en interface &amp;
visualisation</title>, <title xmlns:media="http://search.yahoo.com/mrss/"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:posterous="http://posterous.com/help/rss/1.0"
xmlns:atom="http://www.w3.org/2005/Atom">Hello, world !</title>)
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17. Interpreter
scala> println(
List("Hello","world !") match {
case head :: tail =>
tail.foldLeft(head)(
(a:String,b:String)=>{a+", " +b})})
Hello, world !
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18. Scala – the sublime*
*SUBLIME : pleasure + pain, according to the Romantics
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19. The almost ML-grade type system
val f:List[Int] = List[1,2,3]
val m:Map[String,List[Int]] = Map(
“a” → [1,2,3],
“b” → [4,5,6]
)
type JSONable = { def toJSON():String }
> ensure constraints at compile-type, speed up programs
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20. Multiple method dispatch
def merge( def merge(
a:Map[String,Object], a:List[Object],
b:Map[String,Object] b:List[Object]
):Map[String,Object] ):List[Object]
> makes it easy to specialize (existing) libraries
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21. Pattern-matching
val sum = {
_ match {
case head :: tail >
head + sum (tail)
case Nil >
0
}
}
> amazing for message-based communication and list manipulation
ffunction
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22. Actors
import scala.actors.Actor._
actor {
while (true) {println ("Hello from A") ; Thread.sleep(1)}
}
actor {
while (true) {println ("Hello from B") ; Thread.sleep(1)}
}
Hello from A Hello from A Hello from A Hello from A Hello from A Hello from A
Hello from A Hello from A Hello from A Hello from A Hello from A Hello from A
Hello from B Hello from B Hello from B Hello from B Hello from B Hello from B
Hello from A Hello from A Hello from A Hello from A Hello from A Hello from A
Hello from B Hello from B Hello from B Hello from B Hello from B Hello from B
Hello from A Hello from A Hello from A Hello from A Hello from A Hello from A
Hello from B Hello from B Hello from B Hello from B Hello from B Hello from B
Hello from A Hello from A Hello from A Hello from A Hello from A Hello from A
Hello from B Hello from B Hello from B Hello from B Hello from B Hello from B
Hello from A Hello from A Hello from A Hello from A Hello from A Hello from A
Hello from B Hello from B Hello from B Hello from B Hello from B Hello from B
Hello from A Hello from A Hello from A Hello from A Hello from A Hello from A
Hello from B Hello from B Hello from B Hello from B Hello from B Hello from B
Hello from A Hello from A Hello from A Hello from A Hello from A Hello from A
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23. Message-passing
import scala.actors.Actor._
val repeater = actor {
while (true) {
receive {
case msg:String =>
println(this + ">" + msg) ; reply (msg)
}}}
actor {
repeater ! "ping"
while (true) { receive {
case msg:String =>
println(this + ">" + msg) ; reply (msg)
}}}
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24. Le mot de la fin
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25. Scala is cool !
●
Very powerful
●
Hard to learn, long time to master
●
Amazing complement to Python for research &
performance-critical and scalable projects
●
Easy to interface with Python !
ffunction
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26. Merci !
www.ffctn.com
sebastien@ffctn.com
ffunction
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