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Scala example source code file (WordCount.scala)

This example Scala source code file (WordCount.scala) is included in the "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Scala by Example" TM.

Learn more about this Scala project at its project page.

Java - Scala tags/keywords

array, boolean, char, count, int, state, wordcount

The WordCount.scala Scala example source code

package scalaz.example

import scalaz.{Monoid, StateT}

 * Character/Line/Word Count from "The Essense of the Iterator Pattern".
 * @see [[]]
object WordCount {
  def main(args: Array[String]) = {

  def wordCount {
    import scalaz.State

    val text = "the cat in the hat\n sat on the mat\n".toList

    import scalaz.std.anyVal._, scalaz.std.list._, scalaz.std.boolean.test,

    // To count words, we need to detect transitions from whitespace to non-whitespace.
    // atWordStart_{i} = heaviside( test(isSpace(c_{i}) - test(isSpace(c_{i-1})) )
    def atWordStart(c: Char): State[Boolean, Int] = State { (prev: Boolean) =>
      val cur = c != ' '
      (cur, test(cur && !prev))

    // To count, we traverse with a function returning 0 or 1, and sum the results
    // with Monoid[Int], packaged in a constant monoidal applicative functor.
    val Count = Monoid[Int].applicative

    // Compose the applicative instance for [a]State[Boolean,a] with the Count applicative
    val WordCount = StateT.stateMonad[Boolean].compose[λ[α=>Int]](Count)

    // Fuse the three applicatives together in parallel...
    val A = Count

    // ... and execute them in a single traversal
    val ((charCount, lineCount), wordCountState) = A.traverse(text)((c: Char) => ((1, test(c == '\n')), atWordStart(c)))
    val wordCount = wordCountState.eval(false)

    println("%d\t%d\t%d\t".format(lineCount, wordCount, charCount)) // 2	9	35

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