For-comprehensions article updated with tabs

Author: anatoliykmetyuk

Diff for: _tour/for-comprehensions.md

@@ -16,6 +16,8 @@ Scala offers a lightweight notation for expressing *sequence comprehensions*. Co
 
 Here's an example:
 
+{% tabs for-comprehensions-01 class=tabs-scala-version %}
+{% tab 'Scala 2' for=for-comprehensions-01 %}
 ```scala mdoc
 case class User(name: String, age: Int)
 
@@ -31,23 +33,65 @@ val twentySomethings =
 
 twentySomethings.foreach(println)  // prints Travis Dennis
 ```
+{% endtab %}
+
+{% tab 'Scala 3' for=for-comprehensions-01 %}
+```scala
+case class User(name: String, age: Int)
+
+val userBase = List(
+  User("Travis", 28),
+  User("Kelly", 33),
+  User("Jennifer", 44),
+  User("Dennis", 23))
+
+val twentySomethings =
+  for user <- userBase if user.age >=20 && user.age < 30
+  yield user.name  // i.e. add this to a list
+
+twentySomethings.foreach(println)  // prints Travis Dennis
+```
+{% endtab %}
+{% endtabs %}
+
 
 A `for` loop with a `yield` statement returns a result, the container type of which is determined by the first generator. `user <- userBase` is a `List`, and because we said `yield user.name` where `user.name` is a `String`, the overall result is a `List[String]`. And `if user.age >=20 && user.age < 30` is a guard that filters out users who are not in their twenties.
 
 Here is a more complicated example using two generators. It computes all pairs of numbers between `0` and `n-1` whose sum is equal to a given value `v`:
 
+{% tabs for-comprehensions-02 class=tabs-scala-version %}
+{% tab 'Scala 2' for=for-comprehensions-02 %}
 ```scala mdoc
 def foo(n: Int, v: Int) =
    for (i <- 0 until n;
         j <- 0 until n if i + j == v)
    yield (i, j)
 
-foo(10, 10) foreach {
+foo(10, 10).foreach {
   case (i, j) =>
     println(s"($i, $j) ")  // prints (1, 9) (2, 8) (3, 7) (4, 6) (5, 5) (6, 4) (7, 3) (8, 2) (9, 1)
 }
 
 ```
+
+{% endtab %}
+
+{% tab 'Scala 3' for=for-comprehensions-02 %}
+```scala
+def foo(n: Int, v: Int) =
+   for  i <- 0 until n
+        j <- 0 until n if i + j == v
+   yield (i, j)
+
+foo(10, 10).foreach {
+  case (i, j) =>
+    println(s"($i, $j) ")  // prints (1, 9) (2, 8) (3, 7) (4, 6) (5, 5) (6, 4) (7, 3) (8, 2) (9, 1)
+}
+
+```
+{% endtab %}
+{% endtabs %}
+
 Here `n == 10` and `v == 10`. On the first iteration, `i == 0` and `j == 0` so `i + j != v` and therefore nothing is yielded. `j` gets incremented 9 more times before `i` gets incremented to `1`. Without the `if` guard, this would simply print the following:
 ```scala
 (0, 0) (0, 1) (0, 2) (0, 3) (0, 4) (0, 5) (0, 6) (0, 7) (0, 8) (0, 9) (1, 0) ...
@@ -57,6 +101,8 @@ Note that comprehensions are not restricted to lists. Every datatype that suppor
 
 You can omit `yield` in a comprehension. In that case, comprehension will return `Unit`. This can be useful in case you need to perform side-effects. Here's a program equivalent to the previous one, but without using `yield`:
 
+{% tabs for-comprehensions-03 class=tabs-scala-version %}
+{% tab 'Scala 2' for=for-comprehensions-03 %}
 ```scala mdoc:nest
 def foo(n: Int, v: Int) =
    for (i <- 0 until n;
@@ -65,6 +111,20 @@ def foo(n: Int, v: Int) =
 
 foo(10, 10)
 ```
+{% endtab %}
+
+{% tab 'Scala 3' for=for-comprehensions-03 %}
+```scala
+def foo(n: Int, v: Int) =
+   for  i <- 0 until n
+        j <- 0 until n if i + j == v
+   do println(s"($i, $j)")
+
+foo(10, 10)
+```
+{% endtab %}
+{% endtabs %}
+
 
 ## More resources