Task: Rosetta Code_Rank languages by popularity
C#: using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Text.RegularExpressions;

class Program
{
    static void Main(string[] args)
    {
        string get1 = new WebClient().DownloadString("http:
        string get2 = new WebClient().DownloadString("http:

        ArrayList langs = new ArrayList();
        Dictionary<string, int> qtdmbr = new Dictionary<string, int>();

        MatchCollection match1 = new Regex("\"title\":\"Category:(.+?)\"").Matches(get1);
        MatchCollection match2 = new Regex("title=\"Category:(.+?)\">.+?</a>[^(]*\\((\\d+) members\\)").Matches(get2);

        foreach (Match lang in match1) langs.Add(lang.Groups[1].Value);

        foreach (Match match in match2)
        {
            if (langs.Contains(match.Groups[1].Value))
            {
                qtdmbr.Add(match.Groups[1].Value, Int32.Parse(match.Groups[2].Value));
            }
        }

        string[] test = qtdmbr.OrderByDescending(x => x.Value).Select(x => String.Format("{0,3} - {1}", x.Value, x.Key)).ToArray();

        int count = 1;

        foreach (string i in test)
        {
            Console.WriteLine("{0,3}. {1}", count, i);
            count++;
        }
    }
}

Go: package main

import (
	"encoding/xml"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"net/url"
	"regexp"
	"sort"
	"strconv"
	"strings"
)

var baseQuery = "http:
	"&format=xml&list=categorymembers&cmlimit=500"

func req(u string, foundCm func(string)) string {
	resp, err := http.Get(u)
	if err != nil {
		log.Fatal(err) 
	}
	defer resp.Body.Close()
	for p := xml.NewDecoder(resp.Body); ; {
		t, err := p.RawToken()
		switch s, ok := t.(xml.StartElement); {
		case err == io.EOF:
			return ""
		case err != nil:
			log.Fatal(err)
		case !ok:
			continue
		case s.Name.Local == "cm":
			for _, a := range s.Attr {
				if a.Name.Local == "title" {
					foundCm(a.Value)
				}
			}
		case s.Name.Local == "categorymembers" && len(s.Attr) > 0 &&
			s.Attr[0].Name.Local == "cmcontinue":
			return url.QueryEscape(s.Attr[0].Value)
		}
	}
	return ""
}


type pop struct {
	string
	int
}
type popList []pop

func (pl popList) Len() int      { return len(pl) }
func (pl popList) Swap(i, j int) { pl[i], pl[j] = pl[j], pl[i] }
func (pl popList) Less(i, j int) bool {
	switch d := pl[i].int - pl[j].int; {
	case d > 0:
		return true
	case d < 0:
		return false
	}
	return pl[i].string < pl[j].string
}

func main() {
	
	langMap := make(map[string]bool)
	storeLang := func(cm string) {
		if strings.HasPrefix(cm, "Category:") {
			cm = cm[9:]
		}
		langMap[cm] = true
	}
	languageQuery := baseQuery + "&cmtitle=Category:Programming_Languages"
	continueAt := req(languageQuery, storeLang)
	for continueAt != "" {
		continueAt = req(languageQuery+"&cmcontinue="+continueAt, storeLang)
	}
	
	s := make(popList, 0, len(langMap))

	
	resp, err := http.Get("http:
		"?title=Special:Categories&limit=5000")
	if err != nil {
		log.Fatal(err)
	}
	page, err := ioutil.ReadAll(resp.Body)
	resp.Body.Close()

	
	rx := regexp.MustCompile("<li><a.*>(.*)</a>.*[(]([0-9]+) member")
	for _, sm := range rx.FindAllSubmatch(page, -1) {
		ls := string(sm[1])
		if langMap[ls] {
			if n, err := strconv.Atoi(string(sm[2])); err == nil {
				s = append(s, pop{ls, n})
			}
		}
	}

	
	sort.Sort(s)
	lastCnt, lastIdx := -1, 1
	for i, lang := range s {
		if lang.int != lastCnt {
			lastCnt = lang.int
			lastIdx = i + 1
		}
		fmt.Printf("%3d. %3d - %s\n", lastIdx, lang.int, lang.string)
	}
}