The first() function on a List is an example of functional programming.

first() is a function that takes a lambda expression as a parameter. A lambda expression is simply a way of representing an anonymous function. first() uses the lambda expression, calling it to evaluate the items in the list. Specifically, first() iterates through the list until the lambda expression returns true for an item in the list (or until first() reaches the end of the list).

Functions like first() are called higher-order functions: functions that take functions (e.g., lambda expressions) as parameters.

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• Elements of Kotlin