Practice

Scala exercises

Make a change, predict what it will do, and compare the result.

1
Scala Basics
Run a small program with an entry point.
Adapt the lesson example. Change one value or element, predict the result, and explain why it changes.
Review lesson →Open compiler
Show starting example
Scala
```
object Main {
  def main(args: Array[String]): Unit = {
    val name = "Ada"
    println(s"Hello, $name")
  }
}
```
2
Scala Functions as Values
Define a method and pass it to a higher-order function.
Predict twice(square, 2).
Reveal answer and reasoning
square(2) is 4 and square(4) is 16.
Review lesson →Open compiler
Show starting example
Scala
```
object Main {
  def square(n: Int): Int = n * n

  def main(args: Array[String]): Unit = {
    val twice = (f: Int => Int, x: Int) => f(f(x))
    println(square(5))
    println(twice(square, 3))
  }
}
```

Scala Case Classes and Pattern Matching

Define a data class and take it apart with match.

Add a case for points on the y-axis.

Reveal answer and reasoning

Add case Point(0, y) => s"on y-axis at $y" before the catch-all.

Review lesson →Open compiler

Show starting example

Scala

object Main {
  case class Point(x: Int, y: Int)

  def describe(p: Point): String = p match {
    case Point(0, 0) => "origin"
    case Point(x, 0) => s"on x-axis at $x"
    case _ => "elsewhere"
  }

  def main(args: Array[String]): Unit = {
    println(describe(Point(0, 0)))
    println(describe(Point(4, 0)))
    println(describe(Point(1, 2)))
  }
}

4
Scala Collections: map and filter
Transform and filter an immutable List without loops.
Predict scores.filter(s => s > 80).
Reveal answer and reasoning
It keeps 82 and 91, giving List(82, 91).
Review lesson →Open compiler
Show starting example
Scala
```
object Main {
  def main(args: Array[String]): Unit = {
    val scores = List(82, 91, 76)
    val curved = scores.map(s => s + 5)
    println(curved)
    println(curved.filter(s => s >= 90).sum)
  }
}
```
5
Scala Maps and Option
Look up a key without nulls by using Option.
Predict ages.get("Grace").map(a => a + 1).
Reveal answer and reasoning
Some(46); map applies the function only when a value is present.
Review lesson →Open compiler
Show starting example
Scala
```
object Main {
  def main(args: Array[String]): Unit = {
    val ages = Map("Ada" -> 36, "Grace" -> 45)
    println(ages.get("Ada"))
    println(ages.get("Linus"))
    println(ages.getOrElse("Linus", 0))
  }
}
```

Scala Basics

Scala Functions as Values

Scala Case Classes and Pattern Matching

Scala Collections: map and filter

Scala Maps and Option