Question

I’m basically new to functional programming and scala, and the following question might possibly look stupid.

val f = (a:Int) => a+1

In the above snippet, should I consider f to be a function or a variable? Coming from a C/C++ background, the first thought that occurs is that f is a variable that stores the return value of the anonymous function, but I think that’s not the correct way to interpret it Any explanation would be really helpful.

(Some of the terminologies I used above might be wrong with respect to scala/functional programming, kindly bear with it)

Answer 1

Here, f is a variable that stores a function. It’s really no different from saying any of the following:

val a = 4               // `a` is a variable storing an Int
val b = "hi"            // `b` is a variable storing a String
val f = (a:Int) => a+1  // `f` is a variable storing a function

You can also confirm this with the REPL:

scala> val f = (a:Int) => a+1
f: Int => Int = <function1>

So this is telling you that f has the type Int => Int. Or in other words, f is a function that takes one argument, an Int, and returns an Int.

Since f is a variable, you can call methods on it or pass it as an argument to functions that expect its type:

a + 3  // here I'm calling the `+` method on `a`, which is an Int
f(3)   // here I'm calling the `apply` method on `f`, which is a function `Int => Int`
f(a)   // the function `f` expects an `Int`, which `a` is
(1 to 3).map(f)  // the `map` method expects a function from Int to Int, like `f`