A function can be either total or partial. In this presentation, we explain how we can create and use partial functions from Scala code.

1. Par$al
Func$ons
in
Scala

2. Total
vs.
Par$al
• Total
func$on:
defined
for
all
values
in
its
domain
a x b
• Par(al
func$on:
defined
for
some
values
in
its
domain
a ÷ b

3. Total
func$ons
in
Scala
def mult(a: Int, b: Int) = a * b
scala> mult(5,42)
res0: Int = 220

4. Par$al
Func$ons
def div(a: Int, b: Int) = a / b
scala> div(1,0)
java.lang.ArithmeticException: / by zero

5. Par$al
Func$ons
val safeDiv: PartialFunction[(Int,Int),Int] = {
case (a,b) if b != 0 => a/b
}
scala> safeDiv(1,0)
scala.MatchError: (1,0)
scala> safeDiv.isDefinedAt (1,0)
false

6. Combining
Par$al
Func$ons
safeDiv orElse defaultDiv

7. Par$al
Func$ons
in
disguise
val map = Map(1 -> "One", 2 -> "Two")
map(1) //One
map(10) // NoSuchElementException: key
not found: 10
map.isDefinedAt(1) // true
map.isDefinedAt(10) //false

8. Par$al
Func$ons
in
disguise
• List
• Seq
• Range