Throughout the previous sections, we discussed Kotlin's approach to null safety. But this is not the only approach. Languages such as Haskell have provided an alternative for many years. In Haskell's case, this is called the Maybe type. In Scala there is something similar called the Option type, and in the most recent version of Java (at the time of writing, Java 8) there is Optional.

All of these types—Maybe, Option, Optional—aim to do the same thing. That is, they use a type to indicate that a function or expression may or may not return a value.

In functional programming, they are most often an algebraic data type with two values—one that represents a value and one that represents the lack of a value. In Haskell they are called Just and Nothing. In Scala they are called Some and None. In Java only a single type is used.

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