Code Examples for

Programming in Scala

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2 First Steps in Scala

Sample run of chapter's interpreter examples

Step 1. Learn to use the Scala interpreter

$ scala Welcome to Scala version 2.7.2. Type in expressions to have them evaluated. Type :help for more information. scala>
scala> 1 + 2
res0: Int = 3
scala> res0 * 3 res1: Int = 9
scala> println("Hello, world!") Hello, world!

Step 2. Define some variables

scala> val msg = "Hello, world!" msg: java.lang.String = Hello, world!
scala> val msg2: java.lang.String = "Hello again, world!" msg2: java.lang.String = Hello again, world!
scala> val msg3: String = "Hello yet again, world!" msg3: String = Hello yet again, world!
scala> println(msg) Hello, world!
scala> msg = "Goodbye cruel world!" <console>:5: error: reassignment to val msg = "Goodbye cruel world!" ^
scala> var greeting = "Hello, world!" greeting: java.lang.String = Hello, world!
scala> greeting = "Leave me alone, world!" greeting: java.lang.String = Leave me alone, world!
scala> val multiLine = \| "This is the next line." multiLine: java.lang.String = This is the next line.
scala> val oops = \| \| You typed two blank lines. Starting a new command. scala>

Step 3. Define some functions

scala> def max(x: Int, y: Int): Int = { | if (x > y) x | else y | } max: (Int,Int)Int
scala> def max2(x: Int, y: Int) = if (x > y) x else y max2: (Int,Int)Int
scala> max(3, 5) res6: Int = 5
scala> def greet() = println("Hello, world!") greet: ()Unit
scala> :quit $

Step 4. Write some Scala scripts

println("Hello, world, from a script!")
$ scala hello.scala
Hello, world, from a script!
// Say hello to the first argument println("Hello, "+ args(0) +"!")
$ scala helloarg.scala planet
Hello, planet!

Step 5. Loop with while; decide with if

var i = 0 while (i < args.length) { println(args(i)) i += 1 }
$ scala printargs.scala Scala is fun
Scala is fun
var i = 0 while (i < args.length) { if (i != 0) print(" ") print(args(i)) i += 1 } println()
$ scala echoargs.scala Scala is even more fun
Scala is even more fun
var i = 0; while (i < args.length) { if (i != 0) { print(" "); } print(args(i)); i += 1; } println();

Step 6. Iterate with foreach and for

args.foreach(arg => println(arg))
$ scala pa.scala Concise is nice
Concise is nice
args.foreach((arg: String) => println(arg))
for (arg <- args) println(arg)
$ scala forargs.scala for arg in args
for arg in args

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