Sample run of chapter's interpreter examples
def elements: Iterator[A]
def hasNext: Boolean def next: A
scala> val colors = List("red", "blue", "green") colors: List[java.lang.String] = List(red, blue, green) scala> colors.head res0: java.lang.String = red scala> colors.tail res1: List[java.lang.String] = List(blue, green)
scala> val fiveInts = new Array[Int](5) fiveInts: Array[Int] = Array(0, 0, 0, 0, 0)
scala> val fiveToOne = Array(5, 4, 3, 2, 1) fiveToOne: Array[Int] = Array(5, 4, 3, 2, 1)
scala> fiveInts(0) = fiveToOne(4) scala> fiveInts res1: Array[Int] = Array(1, 0, 0, 0, 0)
scala> import scala.collection.mutable.ListBuffer import scala.collection.mutable.ListBuffer scala> val buf = new ListBuffer[Int] buf: scala.collection.mutable.ListBuffer[Int] = ListBuffer() scala> buf += 1 scala> buf += 2 scala> buf res11: scala.collection.mutable.ListBuffer[Int] = ListBuffer(1, 2) scala> 3 +: buf res12: scala.collection.mutable.Buffer[Int] = ListBuffer(3, 1, 2) scala> buf.toList res13: List[Int] = List(3, 1, 2)
scala> import scala.collection.mutable.ArrayBuffer import scala.collection.mutable.ArrayBuffer
scala> val buf = new ArrayBuffer[Int]() buf: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()
scala> buf += 12 scala> buf += 15 scala> buf res16: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(12, 15)
scala> buf.length res17: Int = 2 scala> buf(0) res18: Int = 12
scala> import scala.collection.immutable.Queue import scala.collection.immutable.Queue scala> val empty = new Queue[Int] empty: scala.collection.immutable.Queue[Int] = Queue()
scala> val has1 = empty.enqueue(1) has1: scala.collection.immutable.Queue[Int] = Queue(1)
scala> val has123 = has1.enqueue(List(2, 3)) has123: scala.collection.immutable.Queue[Int] = Queue(1,2,3)
scala> val (element, has23) = has123.dequeue element: Int = 1 has23: scala.collection.immutable.Queue[Int] = Queue(2,3)
scala> import scala.collection.mutable.Queue import scala.collection.mutable.Queue scala> val queue = new Queue[String] queue: scala.collection.mutable.Queue[String] = Queue() scala> queue += "a" scala> queue ++= List("b", "c") scala> queue res21: scala.collection.mutable.Queue[String] = Queue(a, b, c) scala> queue.dequeue res22: String = a scala> queue res23: scala.collection.mutable.Queue[String] = Queue(b, c)
scala> import scala.collection.mutable.Stack import scala.collection.mutable.Stack scala> val stack = new Stack[Int] stack: scala.collection.mutable.Stack[Int] = Stack() scala> stack.push(1) scala> stack res1: scala.collection.mutable.Stack[Int] = Stack(1) scala> stack.push(2) scala> stack res3: scala.collection.mutable.Stack[Int] = Stack(1, 2) scala> stack.top res8: Int = 2 scala> stack res9: scala.collection.mutable.Stack[Int] = Stack(1, 2) scala> stack.pop res10: Int = 2 scala> stack res11: scala.collection.mutable.Stack[Int] = Stack(1)
scala> def hasUpperCase(s: String) = s.exists(_.isUpperCase) hasUpperCase: (String)Boolean scala> hasUpperCase("Robert Frost") res14: Boolean = true scala> hasUpperCase("e e cummings") res15: Boolean = false
object Predef { type Set[T] = scala.collection.immutable.Set[T] type Map[K, V] = scala.collection.immutable.Map[K, V] val Set = scala.collection.immutable.Set val Map = scala.collection.immutable.Map // ... }
scala> import scala.collection.mutable import scala.collection.mutable
scala> val mutaSet = mutable.Set(1, 2, 3) mutaSet: scala.collection.mutable.Set[Int] = Set(3, 1, 2)
scala> val text = "See Spot run. Run, Spot. Run!" text: java.lang.String = See Spot run. Run, Spot. Run! scala> val wordsArray = text.split("[ !,.]+") wordsArray: Array[java.lang.String] = Array(See, Spot, run, Run, Spot, Run)
scala> val words = mutable.Set.empty[String] words: scala.collection.mutable.Set[String] = Set()
scala> for (word <- wordsArray) | words += word.toLowerCase scala> words res25: scala.collection.mutable.Set[String] = Set(spot, run, see)
scala> val map = mutable.Map.empty[String, Int] map: scala.collection.mutable.Map[String,Int] = Map()
scala> val map = mutable.Map.empty[String, Int] map: scala.collection.mutable.Map[String,Int] = Map()
scala> map("hello") = 1 scala> map("there") = 2 scala> map res28: scala.collection.mutable.Map[String,Int] = Map(hello -> 1, there -> 2)
scala> map("hello") res29: Int = 1
scala> def countWords(text: String) = { | val counts = mutable.Map.empty[String, Int] | for (rawWord <- text.split("[ ,!.]+")) { | val word = rawWord.toLowerCase | val oldCount = | if (counts.contains(word)) counts(word) | else 0 | counts += (word -> (oldCount + 1)) | } | counts | } countWords: (String)scala.collection.mutable.Map[String,Int] scala> countWords("See Spot run! Run, Spot. Run!") res30: scala.collection.mutable.Map[String,Int] = Map(see -> 1, run -> 3, spot -> 2)
scala> import scala.collection.immutable.TreeSet import scala.collection.immutable.TreeSet scala> val ts = TreeSet(9, 3, 1, 8, 0, 2, 7, 4, 6, 5) ts: scala.collection.immutable.SortedSet[Int] = Set(0, 1, 2, 3, 4, 5, 6, 7, 8, 9) scala> val cs = TreeSet('f', 'u', 'n') cs: scala.collection.immutable.SortedSet[Char] = Set(f, n, u)
scala> import scala.collection.immutable.TreeMap import scala.collection.immutable.TreeMap scala> var tm = TreeMap(3 -> 'x', 1 -> 'x', 4 -> 'x') tm: scala.collection.immutable.SortedMap[Int,Char] = Map(1 -> x, 3 -> x, 4 -> x) scala> tm += (2 -> 'x') scala> tm res38: scala.collection.immutable.SortedMap[Int,Char] = Map(1 -> x, 2 -> x, 3 -> x, 4 -> x)
import scala.collection.mutable.{Map, SynchronizedMap, HashMap} object MapMaker { def makeMap: Map[String, String] = { new HashMap[String, String] with SynchronizedMap[String, String] { override def default(key: String) = "Why do you want to know?" } } }
new HashMap[String, String] with SynchronizedMap[String, String]
override def default(key: String) = "Why do you want to know?"
scala> val capital = MapMaker.makeMap capital: scala.collection.mutable.Map[String,String] = Map() scala> capital ++ List("US" -> "Washington", | "Paris" -> "France", "Japan" -> "Tokyo") res0: scala.collection.mutable.Map[String,String] = Map(Paris -> France, US -> Washington, Japan -> Tokyo) scala> capital("Japan") res1: String = Tokyo scala> capital("New Zealand") res2: String = Why do you want to know? scala> capital += ("New Zealand" -> "Wellington") scala> capital("New Zealand") res3: String = Wellington
// In file collections/Misc.scala import scala.collection.mutable val synchroSet = new mutable.HashSet[Int] with mutable.SynchronizedSet[Int]
scala> val people = Set("Nancy", "Jane") people: scala.collection.immutable.Set[java.lang.String] = Set(Nancy, Jane) scala> people += "Bob" <console>:6: error: reassignment to val people += "Bob" ^
scala> var people = Set("Nancy", "Jane") people: scala.collection.immutable.Set[java.lang.String] = Set(Nancy, Jane) scala> people += "Bob" scala> people res42: scala.collection.immutable.Set[java.lang.String] = Set(Nancy, Jane, Bob)
scala> people -= "Jane" scala> people ++= List("Tom", "Harry") scala> people res45: scala.collection.immutable.Set[java.lang.String] = Set(Nancy, Bob, Tom, Harry)
// In file collections/Capitals.scala var capital = Map("US" -> "Washington", "France" -> "Paris") capital += ("Japan" -> "Tokyo") println(capital("France"))
// In file collections/Capitals.scala import scala.collection.mutable.Map // only change needed! var capital = Map("US" -> "Washington", "France" -> "Paris") capital += ("Japan" -> "Tokyo") println(capital("France"))
scala> var roughlyPi = 3.0 roughlyPi: Double = 3.0 scala> roughlyPi += 0.1 scala> roughlyPi += 0.04 scala> roughlyPi res48: Double = 3.14
scala> List(1, 2, 3) res0: List[Int] = List(1, 2, 3) scala> Set('a', 'b', 'c') res1: scala.collection.immutable.Set[Char] = Set(a, b, c) scala> import scala.collection.mutable import scala.collection.mutable scala> mutable.Map("hi" -> 2, "there" -> 5) res2: scala.collection.mutable.Map[java.lang.String,Int] = Map(hi -> 2, there -> 5) scala> Array(1.0, 2.0, 3.0) res3: Array[Double] = Array(1.0, 2.0, 3.0)
scala> import scala.collection.mutable import scala.collection.mutable scala> val stuff = mutable.Set(42) stuff: scala.collection.mutable.Set[Int] = Set(42) scala> stuff += "abracadabra" <console>:7: error: type mismatch; found : java.lang.String("abracadabra") required: Int stuff += "abracadabra" ^
scala> val stuff = mutable.Set[Any](42) stuff: scala.collection.mutable.Set[Any] = Set(42)
scala> val colors = List("blue", "yellow", "red", "green") colors: List[java.lang.String] = List(blue, yellow, red, green)
scala> import scala.collection.immutable.TreeSet import scala.collection.immutable.TreeSet scala> val treeSet = TreeSet(colors) <console>:6: error: no implicit argument matching parameter type (List[java.lang.String]) => Ordered[List[java.lang.String]] was found. val treeSet = TreeSet(colors) ^
scala> val treeSet = TreeSet[String]() ++ colors treeSet: scala.collection.immutable.SortedSet[String] = Set(blue, green, red, yellow)
scala> treeSet.toList res54: List[String] = List(blue, green, red, yellow)
scala> treeSet.toArray res55: Array[String] = Array(blue, green, red, yellow)
scala> import scala.collection.mutable import scala.collection.mutable scala> treeSet res5: scala.collection.immutable.SortedSet[String] = Set(blue, green, red, yellow) scala> val mutaSet = mutable.Set.empty ++ treeSet mutaSet: scala.collection.mutable.Set[String] = Set(yellow, blue, red, green) scala> val immutaSet = Set.empty ++ mutaSet immutaSet: scala.collection.immutable.Set[String] = Set(yellow, blue, red, green)
scala> val muta = mutable.Map("i" -> 1, "ii" -> 2) muta: scala.collection.mutable.Map[java.lang.String,Int] = Map(ii -> 2, i -> 1) scala> val immu = Map.empty ++ muta immu: scala.collection.immutable.Map[java.lang.String,Int] = Map(ii -> 2, i -> 1)
// In file collections/Misc.scala (1, "hello", Console)
def longestWord(words: Array[String]) = { var word = words(0) var idx = 0 for (i <- 1 until words.length) if (words(i).length > word.length) { word = words(i) idx = i } (word, idx) }
scala> val longest = | longestWord("The quick brown fox".split(" ")) longest: (String, Int) = (quick,1)
scala> longest._1 res56: String = quick scala> longest._2 res57: Int = 1
scala> val (word, idx) = longest word: String = quick idx: Int = 1 scala> word res58: String = quick
scala> val word, idx = longest word: (String, Int) = (quick,1) idx: (String, Int) = (quick,1)
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