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2 First Steps in Scala

Sample run of chapter's interpreter examples

• Step 1. Learn to use the Scala REPL
• 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-do

Step 1. Learn to use the Scala REPL

  $ scala
  Starting Scala REPL...
  scala> 


  scala> 1 + 2


  val res0: Int = 3


  scala> res0 * 3
  val res1: Int = 9


  scala> println("Hello, world!")
  Hello, world!


  

Step 2. Define some variables

  scala> val msg = "Hello, world!"
  val msg: String = Hello, world!


  scala> val msg2: java.lang.String = "Hello again, world!"
  val msg2: 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!"
  1 |msg = "Goodbye cruel world!"
    |^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |Reassignment to val msg



  scala> var greeting = "Hello, world!"
  var greeting: String = Hello, world!


  scala> greeting = "Leave me alone, world!"
  greeting: String = Leave me alone, world!


  scala> val multiLine =
       \|   "This is the next line."
  multiLine: String = This is the next line.


  scala> val oops =
       \| 
       \| 
  You typed two blank lines.  Starting a new command.

  scala>


  

Step 3. Define some functions

  def max(x: Int, y: Int): Int =
    if x > y then x
    else y


  def max(x: Int, y: Int) = if x > y then x else y


  val bigger = max(3, 5) // 5


  scala> def greet() = println("Hello, world!")
  def greet(): Unit


  scala> :quit
  $


  

Step 4. Write some Scala scripts

// In file first-steps-in-scala/hello.scala

  @main def m() =
    println("Hello, world, from a script!")


  $ scala hello.scala


  Hello, world, from a script!


// In file first-steps-in-scala/helloarg.scala

  @main def m(args: String*) =
    // Say hello to the first argument
    println("Hello, " + args(0) + "!")


  $ scala helloarg.scala planet


  Hello, planet!


  

Step 5. Loop with while; decide with if

// In file first-steps-in-scala/printargs.scala

  @main def m(args: String*) =
    var i = 0
    while i < args.length do
      println(args(i))
      i += 1


  $ scala printargs.scala Scala is fun


  Scala
  is
  fun


// In file first-steps-in-scala/echoargs.scala

  @main def m(args: String*) =
    var i = 0
    while i < args.length do
      if i != 0 then
        print(" ")
      print(args(i))
      i += 1
    println()


  $ scala echoargs.scala Scala is even more fun


  Scala is even more fun


// In file first-steps-in-scala/withsemis.scala

  @main def m(args: String*) = {
    var i = 0;
    while (i < args.length) {
      if (i != 0) {
        print(" ");
      }
      print(args(i));
      i += 1;
    }
    println();
  }


  

Step 6. Iterate with foreach and for-do

// In file first-steps-in-scala/pa.scala

  @main def m(args: String*) =
    args.foreach(arg => println(arg))


  $ scala pa.scala Concise is nice


  Concise
  is
  nice


// In file first-steps-in-scala/epa.scala

  @main def m(args: String*) =
    args.foreach((arg: String) => println(arg))


// In file first-steps-in-scala/foreach.scala

  @main def m(args: String*) =
    args.foreach(println)


// In file first-steps-in-scala/forargs.scala

  @main def m(args: String*) =
    for arg <- args do
      println(arg)


  $ scala forargs.scala for arg in args


  for
  arg
  in
  args