Scala 编程风格练习

Question

我最近开始阅读“Exercises in programming style”这本书，其中一项任务是用您选择的语言实现每种编程风格。我决定使用 Scala（我对它还很陌生）并且我已经坚持使用第一种 "good old school" 风格。约束是：

Very small amount of primary memory, typically orders of magnitude smaller than the data that needs to be processed/generated. (The example sets the limit to 1024 cells)

No labels -- i.e. no variable names or tagged memory addresses. All we have is memory that is addressable with numbers.

原始示例（逐行读取文件并计算字数）在 Python 中，如下所示：

data = []
data.append([])    # data[1] is line (max 80 characters)
data.append(None)  # data[2] is index of the start_char of word
data.append(0)     # data[3] is index on characters, i = 0
data.append(False) # data[4] is flag indicating if word was found
data.append('')    # data[5] is the word
data.append('')    # data[6] is word,NNNN
data.append(0)     # data[7] is frequency
...

f = open(sys.argv[1])
# Loop over input file's lines
while True:
    data[1] = [f.readline()]
...

所以我们看到有一些变量（f 和数据），但主要思想是将其保持在最低限度并使用 python 数组作为一堆 "memory addresses".

甚至可以在 Scala 中实现老式编程风格（没有变量名或标记内存地址）吗？具体有没有办法在读取文件内容时避免"line"变量？

for (line <- Source.fromFile("example.txt").getLines) {
  println(line.toUpperCase)
}

将文件内容读入类似于原始示例的数组不起作用，因为它没有提取器（值数据不是大小写class，也不是有一个 unapply/unapplySeq 成员).

P.S。我非常清楚整个任务在 Scala 中可能是 5 行，但这不是重点。

Answer 1

要获取给定文件中的总字数，可以使用以下 Scala 代码：

Source.fromFile("example.txt")
      .getLines.map { line => line.trim.split(" ").length}
      .reduceLeft { _ + _ }

Answer 2

当然你可以避免在 data-array 之外引入变量（并以命令式的方式解决问题）。只需将所有内容放入数组中，而不是将其分配给局部变量。

显然，代码将是一场噩梦，因为数组不会被键入并且您不会为任何数据命名任何有意义的名称，但我假设这就是您的目标这个练习。

import scala.io.Source

/**
 * data 0 : file as line iterator
 * data 1 : index of first unused data cell
 * data 2 : current line
 * data 3 : index of the first letter of the current word
 * data 4 : index of the last letter of the current word
 * data 5 : current word
 * data 6 : temp index to find already initialized words
 * data 7 : flag: Word found
 * data 8, 10, 12, ... words
 * data 9, 11, 13, ... frequencies
 */
object GoodOldSchool {
  def main(args: Array[String]): Unit = {
    val data: Array[Any] = new Array[Any](1024)
    data(0) = Source.fromFile(args(0)).getLines()
    data(1) = 8 // first free cell
    while (data(0).asInstanceOf[Iterator[String]].hasNext) {
      data(2) = data(0).asInstanceOf[Iterator[String]].next()
      data(3) = 0 // index first letter of current word
      data(4) = 0 // index last letter of current word
      // find index last letter of current word
      while (data(4).asInstanceOf[Int] < data(2).asInstanceOf[String].length) {
        // find the next space (we ignore punctuation)
        while (data(4).asInstanceOf[Int] < data(2).asInstanceOf[String].length && data(2).asInstanceOf[String].charAt(data(4).asInstanceOf[Int]) != ' ') {
          data(4) = data(4).asInstanceOf[Int] + 1
        }
        data(5) = data(2).asInstanceOf[String].substring(data(3).asInstanceOf[Int], data(4).asInstanceOf[Int]) // current word
        data(6) = 8 // cell index
        data(7) = false // word already found
        8 until data(1).asInstanceOf[Int] by 2 foreach { _ =>
          // Here, we do a case-sensitive word comparison
          if (data(5) == data(data(6).asInstanceOf[Int])) {
            data(data(6).asInstanceOf[Int] + 1) = data(data(6).asInstanceOf[Int] + 1).asInstanceOf[Int] + 1 // increment frequency
            data(7) = true
          }
          data(6) = data(6).asInstanceOf[Int] + 2
        }
        if (data(7) == false) {
          // create new frequency, because word was not discovered before
          data(data(1).asInstanceOf[Int]) = data(5) // set word
          data(data(1).asInstanceOf[Int] + 1) = 1 // set frequency
          data(1) = data(1).asInstanceOf[Int] + 2 // used up two cells, update index of next free cell
        }
        // move to next word
        data(3) = data(4).asInstanceOf[Int] + 1
        data(4) = data(3)
      }
    }

    data foreach println // let's have a look at our result
  }

}

Scala 编程风格练习

Exercises in programming style with Scala

coding-style

scala