Caoyuan's Blog

FOR, WHILE Is Too Easy, Let's Go Looping

With several 10k code in Erlang, I'm familiar with functional style coding, and I found I can almost rewrite any functions in Erlang to Scala, in syntax meaning.

Now, I have some piece of code written in Java, which I need to translate them to Scala. Since "for", "while", or "do" statement is so easy in Java, I can find a lot of them in Java code. The problem is, should I keep them in the corresponding "for", "while", "do" in Scala, or, as what I do in Erlang, use recursive function call, or, "loop"?

I sure choose to loop, and since Scala supports recursive function call on functions defined in function body (Erlang doesn't), I choose define these functions' name as "loop", and I tried to write code let "loop" looks like a replacement of "for", "while" etc.

Here's a piece of code that is used to read number string and convert to double, only piece of them.

The Java code:

public class ReadNum {

    private double readNumber(int fstChar, boolean isNeg) {
        StringBuilder out = new StringBuilder(22);
        out.append(fstChar);
        
        double v = '0' - fstChar;
        // the maxima length of number stirng won't exceed 22
        for (int i = 0; i < 22; i++) {
            int c = getChar();
            switch (c) {
                case '0':
                case '1':
                case '2':
                case '3':
                case '4':
                case '5':
                case '6':
                case '7':
                case '8':
                case '9':
                    v = v * 10 - (c - '0');
                    out.append(c);
                    continue;
                case '.':
                    out.append('.');
                    return readFrac(out, 22 - i);
                case 'e':
                case 'E':
                    out.append(c);
                    return readExp(out, 22 - i);
                default:
                    if (c != -1) backup(1);
                    if (!isNeg) return v; else return -v
            }
        }
        return 0;
    }
}

The Scala code:

class ReadNum {
   private
   def readNumber(fstChar:Char, isNeg:Boolean) :Double = {
      val out = new StringBuilder(22)
      out.append(fstChar)

      val v:Double = '0' - fstChar
      def loop(c:Char, v:Double, i:Int) :Double = c match {
         // the maxima length of number stirng won't exceed 22
         case _ if i > 21 =>
            0
         case '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' =>
            out.append(c)
            val v1 = v * 10 - (c - '0')
            loop(getChar, v1, i + 1)
         case '.' =>
            out.append('.')
            readFrac(out, 22 - i)
         case 'e' | 'E' =>
            out.append(c)
            readExp(out, 22 - i)
         case _ =>
            if (c != -1) backup(1)
            if (isNeg) v else -v
      }; loop(getChar, v, 1)
   }
}

And yes, I named all these embedded looping function as "loop", every where.

Posted at 09:47AM Oct 22, 2008 by dcaoyuan in Java  |  Comments[6]