Add code tabs to fun-write-method-returns-function

Author: doehyunbaek

Diff for: _overviews/scala3-book/fun-write-method-returns-function.md

@@ -20,48 +20,72 @@ Once again we start with a problem statement:
 Given that statement, you can start building `greet`.
 You know it’s going to be a method:
 
+{% tabs fun-write-method-returns-function-1 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 def greet()
 ```
+{% endtab %}
+{% endtabs %}
 
 You also know this method will return a function that (a) takes a `String` parameter, and (b) prints that string using `println`.
 Therefore that function has the type, `String => Unit`:
 
+{% tabs fun-write-method-returns-function-2 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 def greet(): String => Unit = ???
            ----------------
 ```
+{% endtab %}
+{% endtabs %}
 
 Now you just need a method body.
 You know that the method needs to return a function, and that function takes a `String` and prints it.
 This anonymous function matches that description:
 
+{% tabs fun-write-method-returns-function-3 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 (name: String) => println(s"Hello, $name")
 ```
+{% endtab %}
+{% endtabs %}
 
 Now you just return that function from the method:
 
+{% tabs fun-write-method-returns-function-4 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 // a method that returns a function
 def greet(): String => Unit = 
   (name: String) => println(s"Hello, $name")
 ```
+{% endtab %}
+{% endtabs %}
 
 Because this method returns a function, you get the function by calling `greet()`.
 This is a good step to do in the REPL because it verifies the type of the new function:
 
+{% tabs fun-write-method-returns-function-5 %}
+{% tab 'Scala 2 and 3' %}
 ````
 scala> val greetFunction = greet()
 val greetFunction: String => Unit = Lambda....
     -----------------------------
 ````
+{% endtab %}
+{% endtabs %}
 
 Now you can call `greetFunction`:
 
+{% tabs fun-write-method-returns-function-6 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 greetFunction("Joe")   // prints "Hello, Joe"
 ```
+{% endtab %}
+{% endtabs %}
 
 Congratulations, you just created a method that returns a function, and then executed that function.
 
@@ -72,36 +96,52 @@ Congratulations, you just created a method that returns a function, and then exe
 Our method would be more useful if you could pass in a greeting, so let’s do that.
 All you have to do is pass the greeting in as a parameter to the `greet` method, and use it in the string inside `println`:
 
+{% tabs fun-write-method-returns-function-7 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 def greet(theGreeting: String): String => Unit = 
   (name: String) => println(s"$theGreeting, $name")
 ```
+{% endtab %}
+{% endtabs %}
 
 Now when you call your method, the process is more flexible because you can change the greeting.
 This is what it looks like when you create a function from this method:
 
+{% tabs fun-write-method-returns-function-8 %}
+{% tab 'Scala 2 and 3' %}
 ````
 scala> val sayHello = greet("Hello")
 val sayHello: String => Unit = Lambda.....
     ------------------------
 ````
+{% endtab %}
+{% endtabs %}
 
 The REPL type signature output shows that `sayHello` is a function that takes a `String` input parameter and returns `Unit` (nothing).
 So now when you give `sayHello` a `String`, it prints the greeting:
 
+{% tabs fun-write-method-returns-function-9 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 sayHello("Joe")   // prints "Hello, Joe"
 ```
+{% endtab %}
+{% endtabs %}
 
 You can also change the greeting to create new functions, as desired:
 
+{% tabs fun-write-method-returns-function-10 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 val sayCiao = greet("Ciao")
 val sayHola = greet("Hola")
 
 sayCiao("Isabella")   // prints "Ciao, Isabella"
 sayHola("Carlos")     // prints "Hola, Carlos"
 ```
+{% endtab %}
+{% endtabs %}
 
 
 
@@ -116,27 +156,53 @@ A first thing you know is that you want to create a method that (a) takes a “d
 Furthermore, because that function prints a string that it’s given, you know it has the type `String => Unit`.
 With that information you write the method signature:
 
+{% tabs fun-write-method-returns-function-11 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 def createGreetingFunction(desiredLanguage: String): String => Unit = ???
 ```
+{% endtab %}
+{% endtabs %}
 
 Next, because you know that the possible functions you’ll return take a string and print it, you can write two anonymous functions for the English and French languages:
 
+{% tabs fun-write-method-returns-function-12 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 (name: String) => println(s"Hello, $name")
 (name: String) => println(s"Bonjour, $name")
 ```
+{% endtab %}
+{% endtabs %}
 
 Inside a method it might be a little more readable if you give those anonymous functions some names, so let’s assign them to two variables:
 
+{% tabs fun-write-method-returns-function-13 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 val englishGreeting = (name: String) => println(s"Hello, $name")
 val frenchGreeting = (name: String) => println(s"Bonjour, $name")
 ```
+{% endtab %}
+{% endtabs %}
 
 Now all you need to do is (a) return `englishGreeting` if the `desiredLanguage` is English, and (b) return `frenchGreeting` if the `desiredLanguage` is French.
 One way to do that is with a `match` expression:
 
+{% tabs fun-write-method-returns-function-14 class=tabs-scala-version %}
+{% tab 'Scala 2' for=fun-write-method-returns-function-14 %}
+```scala
+def createGreetingFunction(desiredLanguage: String): String => Unit = {
+  val englishGreeting = (name: String) => println(s"Hello, $name")
+  val frenchGreeting = (name: String) => println(s"Bonjour, $name")
+  desiredLanguage match {
+    case "english" => englishGreeting
+    case "french" => frenchGreeting
+  }
+}
+```
+{% endtab %}
+{% tab 'Scala 3' for=fun-write-method-returns-function-14 %}
 ```scala
 def createGreetingFunction(desiredLanguage: String): String => Unit =
   val englishGreeting = (name: String) => println(s"Hello, $name")
@@ -145,23 +211,33 @@ def createGreetingFunction(desiredLanguage: String): String => Unit =
     case "english" => englishGreeting
     case "french" => frenchGreeting
 ```
+{% endtab %}
+{% endtabs %}
 
 And that’s the final method.
 Notice that returning a function value from a method is no different than returning a string or integer value.
 
 This is how `createGreetingFunction` builds a French-greeting function:
 
+{% tabs fun-write-method-returns-function-16 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 val greetInFrench = createGreetingFunction("french")
 greetInFrench("Jonathan")   // prints "Bonjour, Jonathan"
 ```
+{% endtab %}
+{% endtabs %}
 
 And this is how it builds an English-greeting function:
 
+{% tabs fun-write-method-returns-function-17 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 val greetInEnglish = createGreetingFunction("english")
 greetInEnglish("Joe")   // prints "Hello, Joe"
 ```
+{% endtab %}
+{% endtabs %}
 
 If you’re comfortable with that code---congratulations---you now know how to write methods that return functions.