Functions as first-class values

Let's run to the REPL and try out the following command:

scala> val pred = (y: Int) => y < 10
pred: Int => Boolean = <function1>

The REPL here is saying that pred is a function (<function1>). Scala functions are first-class values. What does this term mean? We can send a first-class value as a parameter to another function, just like we send an integer, a list, or string.

For example, we can find the type of pred just like we can of Int:

scala> val q = 9 
q: Int = 9 
scala> :t q 
Int 
scala> :t pred 
Int => Boolean 

We can send the function pred to a function combinator, as shown in this code snippet:

scala> List(1,11,2,22,3,33) filter(pred) 
res3: List[Int] = List(1, 2, 3)

We can send a function to another function and return a function from another function as follows:

scala> val pred1 = (y: Int) => y < 11 // 1
pred1: Int => Boolean = <function1>

scala> val higher: (Int => Boolean) => (Int...