1.go

package main

import (
  "fmt"
)

type User struct {
  name string
}

func (user User) String() string {
  return fmt.Sprintf("User: name = %s", user.name)
}

func main() {
  user := User{name: "foo"}
  fmt.Println(user)         // User: name = foo
}

2.go

package main

import (
  "fmt"
  "net/http"
)

type User struct {
  name string
}

func (user User) String() string {
  return fmt.Sprintf("User: name = %s", user.name)
}

func (user User) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
  fmt.Fprintf(writer, "hello %s", user.name)
}

func main() {
  user := User{name: "foo"}
  http.ListenAndServe("localhost:8888", user) // visit http://localhost:8888
                                              // receive "hello foo"
}

3.scala

object App {

  case class Post(title: String,
                  body: String,
                  tags: List[String])
  case class Address(street: String,
                     city: String,
                     state: String,
                     zip: String,
                     tags: List[String])

  def formattedTags(taggable: { def tags: List[String] }) = {
    taggable.tags.mkString(",")
  }

  def main(args: Array[String]) {
    val post = Post("Weekly NFL Scores",
                    "This week...",
                    List("news", "sports", "local"))
    println(formattedTags(post))    // news,sports,local

    val address = Address("1 Main St.",
                          "Anytown",
                          "CA",
                          "12345",
                          List("home", "work"))
    println(formattedTags(address)) // home,work
  }
}

4.ml

# let user =
    object
      val name = "foo"
      val friends = []
      method to_json = Printf.sprintf ("{ \"name\" : \"%s\" }") name
      method add_friend friend = friend :: friends
    end;;
val user : < add_friend : 'a -> 'a list; to_json : string > = <obj>

# let movie =
    object
      val title = "Predator"
      val rating = "R"
      method to_json = Printf.sprintf ("{ \"title\" : \"%s\" }") title
      method available user = user#age > 17
    end;;
val movie : < available : < age : int; .. > -> bool; to_json : string > = <obj>

# let serialize jsonable =
    jsonable#to_json
val serialize : < to_json : 'a; .. > -> 'a = <fun

# serialize user;;
- : string = "{ \"name\" : \"foo\" }"

# serialize movie;;
- : string = "{ \"title\" : \"Predator\" }