Task: Mad Libs
C#: using System;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace MadLibs_RosettaCode
{
	class Program
	{
		static void Main(string[] args)
		{
			string madLibs = 
@"Write a program to create a Mad Libs like story.
The program should read an arbitrary multiline story from input.
The story will be terminated with a blank line.
Then, find each replacement to be made within the story, 
ask the user for a word to replace it with, and make all the replacements.
Stop when there are none left and print the final story.
The input should be an arbitrary story in the form:
<name> went for a walk in the park. <he or she>
found a <noun>. <name> decided to take it home.
Given this example, it should then ask for a name, 
a he or she and a noun (<name> gets replaced both times with the same value).";

			StringBuilder sb = new StringBuilder();
			Regex pattern = new Regex(@"\<(.*?)\>");
			string storyLine;
			string replacement;

			Console.WriteLine(madLibs + Environment.NewLine + Environment.NewLine);
			Console.WriteLine("Enter a story: ");

			
			do
			{
				storyLine = Console.ReadLine();
				sb.Append(storyLine + Environment.NewLine);
			} while (!string.IsNullOrEmpty(storyLine) && !string.IsNullOrWhiteSpace(storyLine));

			
			Match nameMatch = pattern.Matches(sb.ToString()).OfType<Match>().Where(x => x.Value.Equals("<name>")).Select(x => x.Value).Distinct() as Match;
			if(nameMatch != null)
			{
				do
				{
					Console.WriteLine("Enter value for: " + nameMatch.Value);
					replacement = Console.ReadLine();
				} while (string.IsNullOrEmpty(replacement) || string.IsNullOrWhiteSpace(replacement));
				sb.Replace(nameMatch.Value, replacement);
			}

			foreach (Match match in pattern.Matches(sb.ToString()))
			{
				replacement = string.Empty;
				
				do
				{
					Console.WriteLine("Enter value for: " + match.Value);
					replacement = Console.ReadLine();
				} while (string.IsNullOrEmpty(replacement) || string.IsNullOrWhiteSpace(replacement));

				int location = sb.ToString().IndexOf(match.Value);
				sb.Remove(location, match.Value.Length).Insert(location, replacement);
			}

			Console.WriteLine(Environment.NewLine + Environment.NewLine + "--[ Here's your story! ]--");
			Console.WriteLine(sb.ToString());
		}
	}
}

Go: package main

import (
    "bufio"
    "fmt"
    "io/ioutil"
    "log"
    "os"
    "regexp"
    "strings"
)

func main() {
    pat := regexp.MustCompile("<.+?>")
    if len(os.Args) != 2 {
        fmt.Println("usage: madlib <story template file>")
        return
    }
    b, err := ioutil.ReadFile(os.Args[1])
    if err != nil {
        log.Fatal(err)
    }
    tmpl := string(b)
    s := []string{}          
    m := map[string]string{} 
    for _, p := range pat.FindAllString(tmpl, -1) {
        if _, ok := m[p]; !ok {
            m[p] = ""
            s = append(s, p)
        }
    }
    fmt.Println("Enter replacements:")
    br := bufio.NewReader(os.Stdin)
    for _, p := range s {
        for {
            fmt.Printf("%s: ", p[1:len(p)-1])
            r, isPre, err := br.ReadLine()
            if err != nil {
                log.Fatal(err)
            }
            if isPre {
                log.Fatal("you're not playing right. :P")
            }
            s := strings.TrimSpace(string(r))
            if s == "" {
                fmt.Println("  hmm?")
                continue
            }
            m[p] = s
            break
        }
    }
    fmt.Println("\nYour story:\n")
    fmt.Println(pat.ReplaceAllStringFunc(tmpl, func(p string) string {
        return m[p]
    }))
}