函数柯里化(Currying)示例

　　”函数柯里化”是指将多变量函数拆解为单变量的多个函数的调用， 可以从高元函数动态地生成大量低元的函数。可以看成一个强大的函数工厂，结合函数式编程，可以叠加出很BT的能力。下面给出了一个示例，说明如何使用 Currying 用一行代码计算任意指数的多项式的和； 以及使用 Currying 实现一个简单的文件处理框架。

　　注意到， Currying 的过程中，参数的顺序是有讲究的。一般， 函数参数建议放在前面，按照想要调用的顺序； 数据参数放在后面。

package scalastudy.basic

import scala.util.matching.Regex
import scala.math.pow
import scalastudy.utils.{PathConstants, DefaultFileUtil}

/**
 * Created by lovesqcc on 16-4-16.
 */
object CurryDemo extends App {

  launch()

  def launch(): Unit = {

    val listNum = 10
    val alist = (1 to listNum).toList

    for (i <- 1 to 3) {
      val listPolySum = polynomialSum(i)(_)
      println(listPolySum(alist))
    }

    val filename = PathConstants.scalaSrcPath + "/basic/CurryDemo.scala"
    val fileContentHandler = handleFile(DefaultFileUtil.readFile)(_)
    val findInFileFunc = fileContentHandler(findInFile)(_)
    println(findInFileFunc(filename))

    val countInFileFunc = fileContentHandler(countInFile)(_)
    println("Non Empty Lines: " + countInFileFunc(filename))
  }

  /*
   * calc 1^m + 2^m + ... + n^m
   */
  def polynomialSum(m: Int)(list: List[Int]): Long = {
      return list.map(pow(_,m)).sum.asInstanceOf[Long];
  }

  def handleFile(filePathHandler:(String) => String)
                (fileContentHandler: (String) => Any)
                (filepath: String): Any = {
      return fileContentHandler(filePathHandler(filepath))
  }

  def findInFile(text:String):Any = {
    val patt = "f\\w+".r
    return patt.findAllIn(text).toList
  }

  def countInFile(text:String):Any = {
    return text.split("\n").toList.filter(s => ! s.matches("^\\s*$")).length
  }

}

package scalastudy.utils

/**
 * Created by lovesqcc on 16-4-16.
 */
object PathConstants {

  val projPath = System.getProperty("user.dir")
  val scalaSrcPath = projPath + "/src/main/java/scalastudy"

}