Iteration with for loops

---
# For loop

```scala
val list = List(1, 8, -3, 12)
```

```scala
for (number <- list) {
 println(s"number is $number")
}
// number is 1
// number is 8
// number is -3
// number is 12
```

---
# Without `s` String interpolator

```scala
val list = List(1, 8, -3, 12)
```

```scala
for (number <- list) {
 println("number is $number")
}
// number is $number
// number is $number
// number is $number
// number is $number
```

---
# Other String interpolators

```scala
println(f"PI is ${Math.PI}%1.2f")
// PI is 3.14
```
]

```scala
val subject = "functional programming"

println(sql"subject = $subject")
// res: Fragment = Fragment("subject = ?")
```

```scala
val names = List("Eda", "Bob")

json"{ names : $names }"
// res: Json = "{ "names" : ["Eda", "Bob"] }"
```
]

---
# Code block: curly braces

```scala
for (number <- list)
 println(s"number is $number")
// number is 1
// number is 8
// number is -3
// number is 12
```
]

```scala
for (number <- list) {
 val square = number * number
 println(s"number square is $square")
}
// number square is 1
// number square is 64
// number square is 9
// number square is 144
```
]

---
# Code block: curly braces

```scala
for (number <- list)
 println(s"number is $number")
// number is 1
// number is 8
// number is -3
// number is 12
```
]

```scala
for (number <- list)
 val square = number * number
 println(s"number square is $square")
// number square is 1
// number square is 64
// number square is 9
// number square is 144
```
]

---
# For loop is a syntax for foreach

.forty-seven-left[
```scala
for (number <- list)
 println(s"number is $number")
// number is 1
// number is 8
// number is -3
// number is 12
```
]

.forty-seven-right[
```scala
list.foreach(number =>
  println(s"number is $number")
)
// number is 1
// number is 8
// number is -3
// number is 12
```
]

```scala
trait List[A] {
  def foreach[To](action: A => To): Unit
}
```

---
# For loop is a syntax for foreach

.forty-seven-left[
```scala
for (number <- list)
 println(s"number is $number")
// number is 1
// number is 8
// number is -3
// number is 12
```
]

.forty-seven-right[
```scala
list.foreach(number =>
  println(s"number is $number")
)
// number is 1
// number is 8
// number is -3
// number is 12
```
]

```scala
trait List[A] {
  def foreach[To](action: A => To): Unit
  def map    [To](update: A => To): List[To]
}
```

---
# For loop is a syntax for foreach

.forty-seven-left[
```scala
for (number <- Point(1, 5))
 println(s"number is $number")
// number is 1
// number is 5
```
]

.forty-seven-right[
```scala
Point(1, 5).foreach(number =>
  println(s"number is $number")
)
// number is 1
// number is 5
```
]

```scala
case class Point(first: Int, second: Int) {
  def foreach[To](action: Int => To): Unit = {
    action(first)
    action(second)
  }
}
```

---
# Nested for loop

```scala
val shapes  = List("triangle", "square")
val colours = List("red", "green", "blue")
```

.forty-seven-left[
```scala
for {
 shape <- shapes
 colour <- colours
} println(s"The $shape is $colour")
// The triangle is red
// The triangle is green
// The triangle is blue
// The square is red
// The square is green
// The square is blue
```
]

.forty-seven-right[
```scala
shapes.foreach{ shape =>
  colours.foreach { colour =>
    println(s"The $shape is $colour")
  }
}
// The triangle is red
// The triangle is green
// The triangle is blue
// The square is red
// The square is green
// The square is blue
```
]

---
# Nested for loop with different data types

```scala
val shapes = List("triangle", "square")
val point  = Point(2, 5)
```

.forty-seven-left[
```scala
for {
 shape <- shapes
 number <- point
} println(s"There is $number ${shape}(s)")
// There is 2 triangle(s)
// There is 5 triangle(s)
// There is 2 square(s)
// There is 5 square(s)
```
]

.forty-seven-right[
```scala
shapes.foreach{ shape =>
  point.foreach { number =>
    println(s"There is $number ${shape}(s)")
  }
}
// There is 2 triangle(s)
// There is 5 triangle(s)
// There is 2 square(s)
// There is 5 square(s)
```
]

---
# Use case

```scala
sum(List(1, 8, -3, 12))
// res: Int = 18
```
]

.forty-seven-right[
<img src="../img/foundation/iteration-for-sum-0.svg" alt="Sum with for loop" style="width:400px;"/>
]