Sample run of chapter's interpreter examples
// In file functions-and-closures/LongLines.scala import scala.io.Source object LongLines { def processFile(filename: String, width: Int) = { val source = Source.fromFile(filename) for (line <- source.getLines()) processLine(filename, width, line) } private def processLine(filename: String, width: Int, line: String) = { if (line.length > width) println(filename + ": " + line.trim) } }
// In file functions-and-closures/LongLines.scala object FindLongLines { def main(args: Array[String]) = { val width = args(0).toInt for (arg <- args.drop(1)) LongLines.processFile(arg, width) } }
$ scala FindLongLines 45 LongLines.scala LongLines.scala: def processFile(filename: String, width: Int) = {
// In file functions-and-closures/LongLines2.scala def processFile(filename: String, width: Int) = { def processLine(filename: String, width: Int, line: String) = { if (line.length > width) println(filename + ": " + line.trim) } val source = Source.fromFile(filename) for (line <- source.getLines()) { processLine(filename, width, line) } }
// In file functions-and-closures/LongLines3.scala import scala.io.Source object LongLines { def processFile(filename: String, width: Int) = { def processLine(line: String) = { if (line.length > width) println(filename + ": " + line.trim) } val source = Source.fromFile(filename) for (line <- source.getLines()) processLine(line) } }
(x: Int) => x + 1
scala> var increase = (x: Int) => x + 1 increase: Int => Int = <function1> scala> increase(10) res0: Int = 11
scala> increase = (x: Int) => x + 9999 increase: Int => Int = <function1> scala> increase(10) res1: Int = 10009
scala> increase = (x: Int) => { | println("We") | println("are") | println("here!") | x + 1 | } increase: Int => Int = <function1> scala> increase(10) We are here! res2: Int = 11
scala> val someNumbers = List(-11, -10, -5, 0, 5, 10) 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) res4: List[Int] = List(5, 10)
scala> someNumbers.filter((x) => x > 0) res5: List[Int] = List(5, 10)
scala> someNumbers.filter(x => x > 0) res6: List[Int] = List(5, 10)
scala> someNumbers.filter(_ > 0) res7: List[Int] = List(5, 10)
scala> someNumbers.filter(x => x > 0) res8: List[Int] = List(5, 10)
scala> val f = _ + _ <console>:7: error: missing parameter type for expanded function ((x$1, x$2) => x$1.$plus(x$2)) val f = _ + _ ^
scala> val f = (_: Int) + (_: Int) f: (Int, Int) => Int = <function2> scala> f(5, 10) res9: Int = 15
// In file functions-and-closures/Misc.scala someNumbers.foreach(println _)
// In file functions-and-closures/Misc.scala someNumbers.foreach(x => println(x))
scala> def sum(a: Int, b: Int, c: Int) = a + b + c sum: (a: Int, b: Int, c: Int)Int
scala> sum(1, 2, 3) res10: Int = 6
scala> val a = sum _ a: (Int, Int, Int) => Int = <function3>
scala> a(1, 2, 3) res11: Int = 6
scala> a.apply(1, 2, 3) res12: Int = 6
scala> val b = sum(1, _: Int, 3) b: Int => Int = <function1>
scala> b(2) res13: Int = 6
scala> b(5) res14: Int = 9
// In file functions-and-closures/Misc.scala someNumbers.foreach(println _)
// In file functions-and-closures/Misc.scala someNumbers.foreach(println)
scala> val c = sum <console>:8: error: missing arguments for method sum; follow this method with `_' if you want to treat it as a partially applied function val c = sum ^ scala> val d = sum _ d: (Int, Int, Int) => Int = <function3> scala> d(10, 20, 30) res14: Int = 60
(x: Int) => x + more // how much more?
scala> (x: Int) => x + more <console>:8: error: not found: value more (x: Int) => x + more ^
scala> var more = 1 more: Int = 1 scala> val addMore = (x: Int) => x + more addMore: Int => Int = <function1> scala> addMore(10) res16: Int = 11
scala> more = 9999 more: Int = 9999 scala> addMore(10) res17: Int = 10009
scala> val someNumbers = List(-11, -10, -5, 0, 5, 10) someNumbers: List[Int] = List(-11, -10, -5, 0, 5, 10) scala> var sum = 0 sum: Int = 0 scala> someNumbers.foreach(sum += _)
scala> sum res19: Int = -11
def makeIncreaser(more: Int) = (x: Int) => x + more
scala> val inc1 = makeIncreaser(1) inc1: Int => Int = <function1> scala> val inc9999 = makeIncreaser(9999) inc9999: Int => Int = <function1>
scala> inc1(10) res20: Int = 11 scala> inc9999(10) res21: Int = 10009
scala> def echo(args: String*) = | for (arg <- args) println(arg) echo: (args: String*)Unit
scala> echo() scala> echo("one") one scala> echo("hello", "world!") hello world!
scala> val arr = Array("What's", "up", "doc?") arr: Array[String] = Array(What's, up, doc?) scala> echo(arr) <console>:10: error: type mismatch; found : Array[String] required: String echo(arr) ^
scala> echo(arr: _*) What's up doc?
scala> def speed(distance: Float, time: Float): Float = | distance / time speed: (distance: Float, time: Float)Float scala> speed(100, 10) res27: Float = 10.0
scala> speed(distance = 100, time = 10) res28: Float = 10.0
scala> speed(time = 10, distance = 100) res29: Float = 10.0
// In file functions-and-closures/NamedDefault.scala def printTime(out: java.io.PrintStream = Console.out) = out.println("time = " + System.currentTimeMillis())
// In file functions-and-closures/NamedDefault.scala def printTime2(out: java.io.PrintStream = Console.out, divisor: Int = 1) = out.println("time = " + System.currentTimeMillis()/divisor)
printTime2(out = Console.err)
printTime2(divisor = 1000)
// In file functions-and-closures/Approximate.scala def approximate(guess: Double): Double = if (isGoodEnough(guess)) guess else approximate(improve(guess))
// In file functions-and-closures/Approximate.scala def approximateLoop(initialGuess: Double): Double = { var guess = initialGuess while (!isGoodEnough(guess)) guess = improve(guess) guess }
// In file functions-and-closures/TailRecursion.scala def boom(x: Int): Int = if (x == 0) 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) throw new Exception("bang!") else bang(x - 1)
scala> bang(5) java.lang.Exception: bang! at .bang(<console>:5) at .<init>(<console>:6) ...
-g:notailcalls
scala> bang(5) java.lang.Exception: bang! at .bang(<console>:5) at .bang(<console>:5) at .bang(<console>:5) at .bang(<console>:5) at .bang(<console>:5) at .bang(<console>:5) at .<init>(<console>:6) ...
// In file functions-and-closures/Misc.scala def isEven(x: Int): Boolean = if (x == 0) true else isOdd(x - 1) def isOdd(x: Int): Boolean = if (x == 0) false else isEven(x - 1)
// In file functions-and-closures/Misc.scala val funValue = nestedFun _ def nestedFun(x: Int) : Unit = { if (x != 0) { println(x); funValue(x - 1) } }
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