NerdeTom: november 2009

Plan

Do it standing, about same mix of slides and coding as before, handouts.

Slide: Tom Waits + install
Slide/Code: fire up scala and show off syntax (REPL)
Slide: motivation
Slide: My verdict + References
Slide/Code: Bonus section

Presentation

“Your hands are like dogs, going to the same places they’ve been. You have to be careful when playing is no longer in the mind but in the fingers, going to happy places. You have to break them of their habits or you don’t explore; you only play what is confident and pleasing. I’m learning to break those habits by playing instruments I know absolutely nothing about, like a bassoon or a waterphone.”—Tom Waits

(Picture from flickr / Conor Lawless).

Install

Download zip-file, unzip, set SCALA_HOME and add to PATH.
Then: install plugins for NetBeans (6.7+, prefer 6.8) and eclipse (3.5+).
I did best letting NetBeans handle project (not Maven).

Syntax / REPL

scala.bat: Quick Read Evaluate Print Loop

Code	Points to make
class PhoneNumber( val kind: String, var no: String ) { override def toString(): String = { no + " (" + kind + ")" } }	switch to name: type val / var / def primary constructor Concise
object PhoneNumber{ def apply( kind: String, no: String ) : PhoneNumber = { new PhoneNumber( kind, no ) } }	object, no statics apply is "default method"
val phonebook = Map( "Tommy mobil" -> PhoneNumber( "cell", "92012201" ), "ICE Medisinsk" -> PhoneNumber( "work", "113" ) )	Expressive
println( phonebook("Tommy mobil" ).no )	Concise
phonebook.foreach(tuple => println( tuple._1 + ":" + tuple._2 ))	High-level functional iteration
1.1.+(2.2) 1 until 10	Pure OO operator mode for methods
val xmlE = <a href="index.html"> {3 + 4} </a> (xmlE \ "@href").text	Pragmatic

Motivation

Evolution, not revolution: Java-like, interoperates with java (seamlessly).

can extend java classes
can implement java interfaces
understands java generics
uses java primitives

Leads you into functional programming.
Easy to do easy stuff, AND facilitates the hard stuff.
More up2date language - builds on java lessons, adds:

Facilitates DSL with several short-hand notations
Traits (~multiple inheritance)
++

One vision (Martin Odersky), not designed by comitee
Pragmatic

"I can honestly say if someone had shown me the Programming Scala book by by Martin Odersky, Lex Spoon & Bill Venners back in 2003 I’d probably have never created Groovy." — James Strachan

"If I were to pick a language to use today other than java, it would be Scala" — James Gosling (from before he left Oracle)

My verdict: lead me into...

Wonderful way of coming from Java to Functional programming. I started out writing java-like OO, but wolfed out by the end of my second 3-hour session.
The book fuelled this transformation.
Scala feels very good so far, I now like Java less...

References

Scala site.

Book "Programming in Scala" (Odersky++) is very good for learning, not so for reference.

The busy Java developer's guide to Scala: articles on DeveloperWorks

From JavaZone 09:

Bonus section

Start with Java Discovery and refactor a suitable class:

common.ServiceDescription (for properties and basics) NB! keep scala-code for equals / canEqual

Show off in code

Code	Points to make
TestServer	object and main
client.v2.Notifier	operators
client.ServiceBrowser: class extends with tryto getReplyDescriptor	traits Function is first-class object Option + match
sclanb.Main.recurse2	Closures, and how crazy I got
sclanb.Main
client.ServiceBrowserListener	abstract, no interface
FirstSwingApp.	DSL, Swing
Code from ch30	Actors

NerdeTom

torsdag 26. november 2009

Scala - learning notes