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2 First Steps in Scala

Sample run of chapter's interpreter examples

• Step 1. Learn to use the Scala interpreter
• Step 2. Define some variables
• Step 3. Define some functions
• Step 4. Write some Scala scripts
• Step 5. Loop with while; decide with if
• Step 6. Iterate with foreach and for

Step 1. Learn to use the Scala interpreter

  $ scala
  Welcome to Scala version 2.8.1.
  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>:6: 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: (x: Int,y: Int)Int


  scala> def max2(x: Int, y: Int) = if (x > y) x else y
  max2: (x: Int,y: Int)Int


  scala> max(3, 5)
  res4: 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))


  args.foreach(println)


  for (arg <- args)
    println(arg)


  $ scala forargs.scala for arg in args


  for
  arg
  in
  args