This post originated from an RSS feed registered with Scala Buzz by Caoyuan Deng. Original Post: FOR, WHILE Is Too Easy, Let's Go Looping Feed Title: Blogs about Scala from Caoyuan Feed URL: http://blogtrader.org/page/dcaoyuan/feed/entries/atom?tags=scala Feed Description: Blogs about Scala from Caoyuan Deng Latest Scala Buzz Posts Latest Scala Buzz Posts by Caoyuan Deng Latest Posts From Blogs about Scala from Caoyuan

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 long 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.