Sample run of chapter's interpreter examples
// In file functions-and-closures/PadLines.scala object Padding: def padLines(text: String, minWidth: Int): String = val paddedLines = for line <- text.linesIterator yield padLine(line, minWidth) paddedLines.mkString("\n") private def padLine(line: String, minWidth: Int): String = if line.length >= minWidth then line else line + " " * (minWidth - line.length)
// In file functions-and-closures/PadLines2.scala def padLines(text: String, minWidth: Int): String = def padLine(line: String, minWidth: Int): String = if line.length >= minWidth then line else line + " " * (minWidth - line.length) val paddedLines = for line <- text.linesIterator yield padLine(line, minWidth) paddedLines.mkString("\n")
// In file functions-and-closures/PadLines3.scala object Padding: def padLines(text: String, minWidth: Int): String = def padLine(line: String): String = if line.length >= minWidth then line else line + " " * (minWidth - line.length) val paddedLines = for line <- text.linesIterator yield padLine(line) paddedLines.mkString("\n")
(x: Int) => x + 1
val increase = (x: Int) => x + 1 increase(10) // 11
val addTwo = (x: Int) => val increment = 2 x + increment addTwo(10) // 12
scala> val someNumbers = List(-11, -10, -5, 0, 5, 10) val someNumbers: List[Int] = List(-11, -10, -5, 0, 5, 10) scala> someNumbers.foreach((x: Int) => println(x)) -11 -10 -5 0 5 10
scala> someNumbers.filter((x: Int) => x > 0) val res4: List[Int] = List(5, 10)
scala> someNumbers.filter((x) => x > 0) val res5: List[Int] = List(5, 10)
scala> someNumbers.filter(x => x > 0) val res6: List[Int] = List(5, 10)
scala> someNumbers.filter(_ > 0) val res7: List[Int] = List(5, 10)
scala> someNumbers.filter(x => x > 0) val res8: List[Int] = List(5, 10)
scala> val f = _ + _ ^ error: missing parameter type for expanded function ((x$1: <error>, x$2) => x$1.$plus(x$2))
scala> val f = (_: Int) + (_: Int) val f: (Int, Int) => Int = $$Lambda$1075/1481958694@289fff3c scala> f(5, 10) val res9: Int = 15
def sum(a: Int, b: Int, c: Int) = a + b + c
sum(1, 2, 3) // 6
val a = sum(_, _, _) // a has type (Int, Int, Int) => Int
a(1, 2, 3) // 6
a.apply(1, 2, 3) // 6
val b = sum(1, _, 3) // b has type Int => Int
b(2) // 6 b(5) // 9
val c = sum // c has type (Int, Int, Int) => Int
c(10, 20, 30) // 60
(x: Int) => x + more // how much more?
scala> (x: Int) => x + more 1 |(x: Int) => x + more | ^^^^ | Not found: more
var more = 1 val addMore = (x: Int) => x + more addMore(10) // 11
more = 9999 addMore(10) // 10009
val someNumbers = List(-11, -10, -5, 0, 5, 10) var sum = 0 someNumbers.foreach(sum += _) sum // -11
def makeIncreaser(more: Int) = (x: Int) => x + more
val inc1 = makeIncreaser(1) val inc9999 = makeIncreaser(9999)
inc1(10) // 11 inc9999(10) // 10009
scala> def echo(args: String*) = | for arg <- args do println(arg) def echo(args: String*): Unit
scala> echo() scala> echo("one") one scala> echo("hello", "world!") hello world!
scala> val seq = Seq("What's", "up", "doc?") val seq: Seq[String] = List(What's, up, doc?) scala> echo(seq) 1 |echo(seq) | ^^^ | Found: (seq : Seq[String]) | Required: String
scala> echo(seq*) What's up doc?
def speed(distance: Float, time: Float) = distance / time speed(100, 10) // 10.0
speed(distance = 100, time = 10) // 10.0
speed(time = 10, distance = 100) // 10.0
// In file functions-and-closures/NamedDefault.scala // In same source file as class Rational object Rational: def apply(numer: Int, denom: Int = 1) = new Rational(numer, denom)
// In file functions-and-closures/NamedDefault.scala def point(x: Int = 0, y: Int = 0) = (x, y)
point(x = 42)
point(y = 1000)
JButton button = new JButton(); // This is Java button.addActionListener( event -> System.out.println("pressed!") );
val button = new JButton button.addActionListener( _ => println("pressed!") )
trait Increaser: def increase(i: Int): Int
def increaseOne(increaser: Increaser): Int = increaser.increase(1)
increaseOne( new Increaser: def increase(i: Int): Int = i + 7 )
increaseOne(i => i + 7) // Scala
// In file functions-and-closures/Approximate.scala def approximate(guess: Double): Double = if isGoodEnough(guess) then guess else approximate(improve(guess))
// In file functions-and-closures/Approximate.scala def approximateLoop(initialGuess: Double): Double = var guess = initialGuess while !isGoodEnough(guess) do guess = improve(guess) guess
// In file functions-and-closures/TailRecursion.scala def boom(x: Int): Int = if x == 0 then throw new Exception("boom!") else boom(x - 1) + 1
scala> boom(3) java.lang.Exception: boom! at .boom(<console>:5) at .boom(<console>:6) at .boom(<console>:6) at .boom(<console>:6) at .<init>(<console>:6) ...
public double approximate(double); Code: 0: aload_0 1: astore_3 2: aload_0 3: dload_1 4: invokevirtual #24; //Method isGoodEnough:(D)Z 7: ifeq 12 10: dload_1 11: dreturn 12: aload_0 13: dload_1 14: invokevirtual #27; //Method improve:(D)D 17: dstore_1 18: goto 2
// In file functions-and-closures/TailRecursion.scala def bang(x: Int): Int = if x == 0 then throw new Exception("bang!") else bang(x - 1)
scala> bang(5) java.lang.Exception: bang! at .bang(<console>:5) at .<init>(<console>:6) ...
// In file functions-and-closures/Misc.scala def isEven(x: Int): Boolean = if x == 0 then true else isOdd(x - 1) def isOdd(x: Int): Boolean = if x == 0 then false else isEven(x - 1)
// In file functions-and-closures/Misc.scala val funValue = nestedFun def nestedFun(x: Int): Unit = if x != 0 then println(x) funValue(x - 1)
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